In 1908, the New York State Legislature created Route 36, an unsigned legislative route that extended from Owego to Seneca Falls via Candor, Ithaca, and Ovid. South of Romulus, Route 36 utilized what is now NY 96 and NY 96B. When the first set of posted routes in New York were assigned in 1924, the Owego–Interlaken and Ovid–Romulus portions of legislative Route 36 became part of NY 15, which began in Owego and proceeded northwest from Romulus to Rochester by way of Waterloo, Phelps, Victor, Mendon, and Pittsford. From Mendon to Rochester, NY 15 followed the path of legislative Route 14, another highway dating back to 1908 that continued south from Mendon on what is now NY 64 and used Monroe Avenue between Pittsford and Rochester. Another section of NY 15—from the village of Phelps east to NY 14—utilized what had been designated as part of legislative Route 6-a from 1911 to 1921.