Highway 15 starts at the Canada-United States border, where it continues as Washington State Route 543. From the border, Highway 15 immediately heads north across 8 Avenue (which provides access to Highway 99. It then continues north towards Cloverdale, but then bypasses the community on the Cloverdale Bypass. While bypassing Cloverdale, Highway 15 intersects with Highway 10. Highway 15 continues north, past the Cloverdale Arena and Fraser Highway, befor ending at an intersection with Highway 1.