U.S. Route 15 (US 15) is a part of the U.S. Highway System that runs from Walterboro, South Carolina, to Painted Post, New York. In the U.S. state of New York, US 15 extends 12.68 miles (20.41 km) through the Southern Tier from the Pennsylvania state line at Lindley north to an interchange with the Southern Tier Expressway (Interstate 86 or I-86 and New York State Route 17 or NY 17) just outside of Painted Post. US 15 originally continued north to Rochester before being truncated to its present northern terminus. All of US 15 in New York will eventually become part of I-99, an Interstate Highway that currently only exists in central Pennsylvania.

US 15 enters New York adjacent to the state line borough of Lawrenceville, Pennsylvania. A four-lane freeway through the Steuben County town of Lindley, US 15 crosses through a rock cut, making a large bend to the north. A short distance later, US 15 leaves the incomplete freeway alignment for local roads, becoming a two-lane arterial through Lindley. Now running north, US 15 intersects with the southern terminus of County Route 120 (CR 120; Morgan Creek Road). The two-lane road winds northeast along the Tioga River, passing through large fields that separate the road and the river. They soon come back together, while US 15 continues north through Lindley. Just after Glick Road, US 15 turns northwest and returns to the limited-access highway alignment, bypassing the hamlet of Presho.

Soon after becoming a limited access highway once again, US 15 enters a partial cloverleaf interchange with CR 5 (Smith Road). After CR 5, US 15 bends northeast through the town of Erwin, running to the west of the Indian Hills Golf Club. Making a gradual bend further to the northeast, the freeway crosses the Canisteo River and enters the hamlet of Erwins, where it enters a diamond interchange with NY 417 (Addison Road). After NY 417, US 15 makes a bend alongside Norfolk Southern Railroad's Southern Tier Line (former Erie Railroad main line). Now paralleling the tracks and NY 417, US 15 crosses through Erwin, entering exit 3, which connects to NY 417 once again, next to Gang Mills Yard, the site of the former Painted Post station.

After Gang Mills Yard, US 15 crosses through the Gang Mills section of Erwins, entering a large interchange at the northern end of the neighborhood. Signed exit 4, this interchange serves CR 107 (Robert Dann Drive) via NY 417. After CR 107, US 15 enters a large interchange that utilizes several flyover ramps between US 15, I-86, and NY 17 (the Southern Tier Expressway). Ramps are also present, connecting to NY 352. This interchange serves as the northern terminus of US 15.

The first set of posted routes in New York were assigned in 1924. One route assigned at this time was NY 4, a highway extending from the Pennsylvania state line in Lindley to downtown Rochester. NY 4 roughly followed the modern alignment of US 15 from Pennsylvania to Presho, Indian Hill Road from Presho to Erwins, NY 417 from Erwins to Gang Mills, and Hamilton Street from Gang Mills to Painted Post. From Painted Post northward, NY 4 was routed along modern NY 415 to Wayland, from where it continued to Rochester on what is now NY 15. At the state line, NY 4 connected to Pennsylvania Route 4 (PA 4). In 1927, US 4 was first signed in New York. As a result, NY 4 was renumbered to NY 2 to eliminate numerical duplication with the new U.S. Highway.

By 1929, US 111 was assigned, following what had been PA 4 northward from Williamsport, Pennsylvania, to the New York state line at Lawrenceville, where it ended. At some point between 1935 and 1937, US 15 was extended northward from Harrisburg, Pennsylvania, to the New York state line by way of an overlap with US 111. The overlap between US 15 and US 111 was eliminated c. 1938 when US 111 was truncated southward to Harrisburg. US 15 was extended northward to Rochester by the following year, replacing all of NY 2.

Construction began c. 1962 on a bypass of NY 17 and US 15 in the vicinity of Corning (modern exit 45) and Painted Post (exit 43). The entirety of the highway, plus an extension northwest to Campbell (exit 41), was completed between 1964 and 1968. US 15 and NY 17 were rerouted to follow the new highway, and their former routings between Campbell and Corning were redesignated as NY 415. The portion of the US 15 / NY 17 freeway between Campbell and Avoca (exit 36) was completed by 1973. In 1974, US 15 was truncated to its current northern terminus in Painted Post and replaced with NY 15 from Painted Post to Rochester.

In the mid-1960s, work began on a limited-access highway paralleling US 15 from Presho to the Southern Tier Expressway at Painted Post. The highway was completed and opened to traffic c. 1969 as a realignment of US 15. The interchange between US 15 and NY 17 (now concurrent with I-86) in Painted Post has been redesigned twice. The original configuration of the interchange featured a loop centered around the point where US 15 met NY 17, with ramps providing access to and from the loop from US 15, NY 17, and North Hamilton Street. The second design, in place until 2003, was a semi-diamond interchange, with US 15 intersecting ramps from I-86 and NY 17 at-grade. One connection, I-86 / NY 17 east to North Hamilton Street, was lost in this version due to the ramp setup of the southern half of the interchange. North of the ramps leading to and from I-86 / NY 17 westbound, the right of way of US 15 continued north into Painted Post as North Hamilton Street. The current setup is a directional T interchange, which creates a freeway-to-freeway connection between US 15 and I-86 / NY 17. Separate ramps for North Hamilton Street from I-86 / NY 17 were retained; however, for the first time, there was no direct connection between US 15 and North Hamilton Street. Work on the interchange began in late 2003 and was completed in mid-2008.

In the National Highway System Designation Act of 1995, the portion of US 15 in New York was defined as part of I-99. I-99 currently ends at I-80; however, construction is either underway or has been completed on projects to upgrade US 220 and US 15 between Bellefonte, Pennsylvania, and Corning to Interstate Highway standards.[citation needed] In June 2007, work began on a new freeway alignment for US 15 between the Pennsylvania state line and Watson Creek Road in Lindley. The highway was opened to traffic on October 1, 2008. Ownership and maintenance of the former surface alignment of US 15 was transferred to Steuben County, which designated the highway as CR 115.

Ground was broken September 21, 2009, on the final section of the freeway between Watson Creek Road and Presho. The $45 million roadbed is expected to be completed by 2012; however, construction of the bridges along the highway—projected to cost another $32.5 million—is not expected to begin until 2012. As a result, the highway is tentatively scheduled to be completed in 2014 or 2015. The bridge portion of the project is receiving $9 million in annual Appalachian Development Highway System (ADHS) funding from 2010 to 2012 and $5.7 million from the state of New York. Local officials have called on state and federal officials to expedite the construction process by paying for the project up front and using ADHS grants in the years to come to pay off the debt later on. The highway was nominated for a Transportation Investment Generating Economic Recovery grant, but was rejected.

The entire route is in Steuben County.