15 minutes from Caribbean Beach to International Gateway is... quite a long time. I've been one to say that these will work with no air conditioning, but it's not like they're gonna be cold. They're gonna have a slight breeze coming in which will be working off of already hot weather so for 15 minutes, this could get rough.
The upside is that they it's a consistently moving mode of transportation rather than waiting 15 minutes for a bus and then driving 15 minutes to a theme park. I'm fascinated at how these will handle a thunder/lightning storm or how early Disney will shut these down prior to a storm reaching the area, though.