@Nerorero

A) 6 Nimmt. scales relatively well with a sweet spot at 4 and 6 players. Takes about 20-40min to play a complete game.
B) One Night Ultimate Werewolf. The first two sets and maybe the bonus roles have lasted us hundreds of iterations. I think it's superior at 5, but other groups like it from 5-8p. Total round/game length is about 10min (almost regardless of player count).
C) For Sale. Skip the expansion, the base game is one of our better higher count options. Total game length is maybe 20min since the second half of the game is simultaneous action selection.

ONUW in particular should go over really well with a LARP group. I do recommend doing index card type role cheatsheets and laminating them. I used to have one that fit in the box but I've lost the photoshop file I made it in... If you get more than about 12 people, then Two Rooms & A Boom works as well and has a ~20min running time. It needs a lot of players though.