From 1927 to the late 1930s, modern NY 15 was part of NY 2. As a result, all of what is now NY 15A was originally designated as New York State Route 2A as part of the 1930 renumbering of state highways in New York. Two parts of the route were sub-standard at the time; however, those sections were rebuilt in the early and mid-1930s. NY 2 was supplanted by an extended US 15 in April 1939, at which time NY 2A was renumbered to NY 15A to match its parent's new designation.