 The U.S. Highway was expanded to four lanes from MD 355 at Harmony Grove to Angleberger Road in Lewistown in 1973.Four-laning of US 15 continued in 1981 when the highway was expanded from the intersection with St. Anthony and Orndorff roads south of Mount St. Mary's University to just south of the Pennsylvania state line near Emmitsburg.This section of divided highway was extended south through the MD 550 interchange in 1983.