Highway 15 begins at an interchange with Highway 401 (Exit 623) in the city of Kingston; it once continued south to former Highway 2 next to CFB Kingston in Barriefield, but this section is now Kingston Road 15. The route travels northeast alongside the Cataraqui River, slicing through Joyceville and passing Joyceville Penitentiary. Over the next several kilometres, the route travels alongside the Rideau Canal, with Locks 43, 44 and 45 a short drive off the highway. After leaving Frontenac County and entering the United Counties of 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.