Successfully completing Chapter 15 opens up a new skirmish map. No insanely angry Valkyria to deal with this time though, “only” a typical enemy base to capture, and a bunch of Imperial grunts in your way.
That’s not to say it’s actually easy. Enemy opposition is pretty heavy this time around. The final few skirmishes are a great way to build up more XP for the endgame content while chasing that elusive A-Ranking.