I have a 6 Plus with a 42mm SS watch and I'm having the exact same issue. Battery life is horrible, 15 mins ago I was at 42% now after some web browsing it went down to 23%. I installed iOS 9 beta as a clean install didn't restore from back up (feating it would carry bugs from iOS 8.4 beta 3) and watchOS 2 beta and battery is draining insanely fast and my phone runs hot too, I'm thinking about downgrading to iOS 8.4 beta 4 seeing if that helps