So you're organising a multi-player session for non Megapack factions? That's great, I love it. I'd love to see more community efforts to get multi-player sessions going in the future (be it Megapack or something else), and I (and probably titi, too) would happily support them by means of placing in-game, website and twitter announcements. I think Annex would also make a good candidate, but I understand it's not on your poll because it's not in the Game mods menu, yet.
15 players is a bunch, though. You may want to settle for less for the first planned multi-player game, after all a server can't take more than 7 network players.