The B2215 is the old A3, before a bigger, three lane by-pass of Ripley and Burntcommon was built. It starts 3 km southwest of Junction 10 of the M25, at a grade-separated junction with the A3, at which it also meets the B2039. It then continues west of the new A3 (this is important) through Ripley village, meeting the B367 and B368 en route.
At Burntcommon, there is a roundabout junction with the A247, and from here the B2215 becomes a dual carriageway - with the particularity, however, that the southbound carriageway fails to make it as far as the A3 at the southwestern end of the bypass, connecting instead only with an unclassified lane to the right, 150 m before the junction. To reach the A3 southbound from Ripley village you needed to have turned left onto the A247 at that last roundabout.
The B2215 has one flaw: its number. It lies entirely to the west of the A3, so shouldn't it really be the B3-something? However, this can be explained by looking at the original route of the B2215, which was as a very short link between the then A3 (now by no sort of coincidence whatsoever, the B2215) to the A247 at Burntcommon. Presumably, the number was moved onto its present route when the current A3 opened, but the original route may have been briefly retained as a short spur before being closed up.