In 1926, U.S. Highway 80 was routed over SH 15. The routes were marked concurrently. On December 16, 1929, SH 15 extended west to Fort Worth. On June 24, 1931, this extension to Fort Worth was cancelled. On September 11, 1934, SH 15 extended west back to Fort Worth. On August 8, 1935, SH 15 was extended west via Albany via Seminole to the Texas-New Mexico boundary, replacing SH 83 and part of SH 1A, though this was not effective until September 1, 1935. On September 26, 1939, the section of SH 15 east of Albany was deleted (already part of US 80 and US 80 Alternate). The remainder of SH 15 was redesignated as US 180 on September 6, 1943.