In addition to Kingston and Carleton Place, the highway provides access to the Eastern Ontario communities of Joyceville, Seeley's Bay, Morton, Elgin, Crosby, Portland, Lombardy and Franktown.

Although realignments and bypasses have been constructed around many of the towns along the route, it continues to serve as a major corridor between Kingston and Ottawa.

A 4.7 km (2.9 mi) segment of the highway, within the town limits of Smiths Falls, is maintained under a Connecting Link agreement.

After leaving Frontenac and entering Leeds and Grenville, the route encounters Seeleys Bay, where it curves east and soon meets the northern terminus of former Highway 32.

It turns north, then crosses between the municipalities of Leeds and the Thousand Islands and Rideau Lakes at the community of Morton.

The route crosses the Rideau Canal and proceeds towards Carleton Place alongside the Ottawa Valley Railway, bisecting the communities of Franktown, Beckwith and Black's Corners.

[note 1] Confederation Square, then known as Connaught Place, was originally planned to serve as the terminus of Ottawa-bound highways when route numbers were posted there in September 1925.

[8] Between Carleton Place and Ottawa, Highway 15 initially followed a circuitous route that served the villages of Ashton and Stittsville.

While the southern end has consistently been within Kingston, the segment north of Smiths Falls has shifted several times, notably in 1961 and 1983.

[16] The bypass, which included a bridge over the Mississippi River and an overpass of what is now the Ottawa Valley Railway, was designated as part of Highway 15 on November 19, 1959.

The Ottawa Board of Trade petitioned the DHO to renumber several highways surrounding the city to accommodate long-distance travellers.

[23] Highway 15 thereafter remained as the sole route connecting Smiths Falls with Carleton Place, Almonte, and Arnprior.

[3] As part of a series of budget cuts initiated by premier Mike Harris under his Common Sense Revolution platform in 1995, numerous highways deemed to no longer be of significance to the provincial network were decommissioned, and responsibility for the routes transferred to a lower level of government, a process referred to as downloading.