The N15 commences halfway across
Lifford Bridge (which crosses the
River Foyle between County Donegal and
County Tyrone), continuing the route of the
A38 (from
Strabane on the east side of the river). In
Lifford, west of the River Foyle, the
N14 meets the N15, ending at a junction in the town centre. The N15 leaves to the southwest, changing to run west at the point just west of
Clady. It continues west through
Castlefin,
Liscooley and
Killygordon to reach
Stranorlar. In Stranorlar, the
N13 commences, leaving the N15 to head north, with the N15 itself turning southwest to cross the
River Finn to enter
Ballybofey. From here, it continues southwest through the mountains and
Barnesmore Gap (passing southeast of the
Bluestack Mountains) towards
Donegal Town. East of the town itself, the
N56 road starts at a junction on the N15 and runs around the north of the town and is the main coastal route for County Donegal, with the N15 then turning to the south, to bypass the eastern side of Donegal Town. The N15 crosses the
Drumenny Burn on the eastern outskirts of Donegal Town. South of Donegal Town, the N15 passes by
Ballintra to the west. Further south, the route follows a road opened in 2006, bypassing
Ballyshannon to the east and crossing the
River Erne on a viaduct. The road enters
County Leitrim directly west of
Bundoran (the bypass passes south of the town).
Tullaghan is the only village along the N15 in the county, also bypassed. The N15 runs closer to the coastline in
County Sligo, passing through
Cliffoney and
Grange as it proceeds southwest. The road then passes through the villages of
Drumcliff and
Rathcormack before entering
Sligo. The route ends at the start of the
N4, which continues through the town as the
Sligo Inner Relief Road dual carriageway. ==Planned and completed upgrades==