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.

Further south, the route follows a road opened in 2006, bypassing Ballyshannon to the east and crossing the River Erne on a viaduct.

A replacement of the current alignment with a new single carriageway road is planned, bypassing Castlefin, Liscooley, and Killygordon.

[4] The project was completed on 17 July 2016[5] Continuing with the N4-N15 Urban Improvements, in August 2019, it was announced that €14 Million had been allocated for a 730-meter upgrade form Hughes bridge to just past the N4-N15-N16 junction.

It would include a six-lane carriageway, improved cycle paths and footpaths, LED streetlights, upgrades on Copper bridge on the N15, and a major redesign of the R291 Rosses Point Junction.

A major repaving of the road from Creevykeel Crossroads to Castelgal was started in mid-October 2019[8] and were very nearly complete before the Covid-19 lockdown happened in Ireland.

[10] In September 2020, Ocean FM Reported that TII allocated between 3 and 4 million Euros to upgrade a stretch of road that is 3.5 Kilometres long between Grange and the townland of Cashelgarran at Henrys Restaurant.