Original designation On July 1, 1919, the original routing of M-15 was located in the
Upper Peninsula (UP). It ran from the state line along the
Menominee River in
Menominee, connecting with
STH-15 in
Wisconsin, running north through the UP to
Escanaba,
Marquette and
Houghton. Between
Powers and Escanaba, M-15 ran concurrently with
M-12. The northern terminus of the highway was at
Fort Wilkins in
Copper Harbor. The first highway centerline in the nation was painted along a section of the highway in 1917, along the Marquette–Negaunee Road, now a part of Marquette County Road 492. The
Peshekee River Bridge, carried M-15 over the
Peshekee River in western Marquette County's
Michigamme Township . The bridge was built in 1914 in response to the 1913 State Trunk Line Act passed by the
Michigan Legislature. This act designated a state trunkline highway network of nearly . The act further said that the
Michigan State Highway Department would design, build and maintain trunkline bridges spanning or more so long as the local governments improved an adjacent of roads. Marquette County built a mainline road from
Marquette west to
Michigamme near the county line, this road generally followed what is now known as County Road 492 (CR 492). About west of Marquette on CR 492 is a historical marker at the site of the first
center line painted in 1917 along Dead Man's Curve. The 1925 draft plan for the establishment of the
US Highway System would have replaced M-15 with three different US Highways. Between Menominee and Powers, M-15 was to be replaced by
US 41. East of Powers to Rapid River, the trunkline would have been US 2. The next segment between Rapid River and
Humboldt was planned as
US 102 while the remainder north to Copper Harbor was not numbered as a US Highway. When the system was announced on November 11, 1926, US 41 was the only US Highway routed along the alignment of M-15. The original map showed US 41 following an unbuilt alignment between Powers and Marquette, but the US 41 designation was instead routed to follow the former M-15.
Current designation The current routing of M-15 was designated after 1926. The southern end was located at
US 10 in Clarkston running north to
M-38 and
M-24 in
Vassar. By June 1942, the M-24 concurrency was removed as M-24 was realigned to replace
M-85 between Vassar and
Caro. By July 1, 1960, the northern end was extended to run concurrently with
M-25 and
BUS US 23 to
US 23 on the west side of Bay City. This M-15/M-25 routing was extended again in the next year to end at the new
I-75/US 10/US 23 freeway. These two northerly extensions were both reversed and scaled back in 1970. M-15's northern end is moved back to M-25/Center Avenue in Bay City, its current location. At some time after the 1993 beginning of the program, M-15 was named the "Pathway to Family Fun" Recreational Heritage Route in what is now the
Pure Michigan Byway System. Running roughly parallel to I-75, the route has not been added to the National Highway System, a system of roadways considered important to the nation's economy, defense and mobility. The state highway map in 1933 showed a proposed southern extension from Clarkston through southern Oakland County,
Wayne County into
Monroe County. This proposed highway would have bypassed
Metro Detroit to the west through
Farmington,
Northville,
Plymouth and
Belleville. The full highway was never built, and M-15 was never extended south of Clarkston, but part of this proposal was completed. Much of it later became Haggerty Highway, and part of the
I-275 and
M-5 corridors. ==Major intersections==