It runs north from Peterborough via Market Deeping, Bourne, Sleaford and Lincoln along a variety of ancient, Roman, and Turnpike alignments before it is interrupted at its junction with the M180 near Scawby.

[2][3] The A15 is Peterborough's main connecting road from the south to the A1(M), joining[4] near Stilton, at Norman Cross.

From here to Yaxley, it passes the Norman Cross Hotel[6] and follows[7] the City of Peterborough and Cambridgeshire boundary, where there is a junction with the B1091 (for Farcet).

The roundabout marks the western end of the £7 million 4-mile (6.4 km) Market Deeping bypass, finished in July 1998.

There is a left turn for Obthorpe and it goes through Thurlby, passing the Horseshoe[17] pub, then Northorpe, before coming to the small town of Bourne.

It meets the B1191 (for Scopwick), B1202 (for Boothby Graffoe to the west and Metheringham to the east) next to the former RAF Coleby Grange, and B1178 (for Harmston), where it passes Dunston Pillar.

A parking place and cafe are provided for plane spotters on the eastern side of the road.

South of Bracebridge Heath, the A15 heads east around the city using the A15 Lincoln Eastern Bypass, a 4.7 miles (7.5 km) single carriageway opened on 19 December 2020.

[39] The A15 then runs unbroken northwestwards to the Riseholme roundabout, where it briefly re-enters the City of Lincoln, then follows[40] the Roman road Ermine Street past the Riseholme College of Agriculture on the right, now part of the University of Lincoln, and Lincolnshire Showground[41] to the left.

From here, it used to be straight, but with RAF Scampton becoming a base for Avro Vulcan V bombers in the 1950s, the runway had to be extended, and the road now has a curved diversion to the east.

It passes the Scampton primary school[47] and continues[48] past a right turn to Normanby by Spital, on its most straight section, also the parish boundary of many local villages.

Overtaking is difficult as the road, although straight, is undulating with unmarked dips and slow-moving farm traffic.

The 5-mile (8.0 km) £7 million Brigg and Redbourne bypass[51] was added in December 1989 which follows[52] the old Ermine Street in North Lincolnshire further than previously, with a much flatter, wider and safer road.

It crosses the Sheffield to Cleethorpes railway line near the deserted village of Gainsthorpe, passes[53] near to Scawby, and joining[54] the M180 at junction 4, near Scunthorpe.

It abandons the Roman alignments at a short spur to the A18 at the Briggate Lodge Roundabout next to the Forest Pines[55] golf club and hotel at Broughton.

Traffic buildup to Grimsby prompted calls for the Brigg bypass for many years, but the Flixborough explosion of 1974 made it more of an emergency.

At junction 5, the A15 reforms at the dual-grade Barnetby Top Interchange, which is crossed by the Viking Way and has an exit to Elsham.

It crosses[66] the A63 and meets a roundabout with A164 (for Beverley) and A1105, then turns left along a short section[67] of dual-carriageway (former A63) to end at the A63.