You have Xerneas on your team, and that's quite powerful on its own; you'd be able to take down two to three Elite Four with it, or perhaps even all four, haha. I'm not absolutely sure, though, as I've personally never used it (well, I did, but only once), but its stats are very high, so judging from them, it should make things a lot easy for you.
As for Charizard, which mega-form will you be using—X or Y? I'd personally recommend latter, as you already have a dragon-type on your team. If I were you, I'd probably replace Hawlucha with it.