I'd personally put out a "Flash" movie in 2015 and wait to put out JL till 2016. I really think this would be there best bet for success. WB needs to familiarize the GP with superheroes other then Sups and Batman before releasing A JL movie. I mean, Thor is my favorite out of all the Marvel hero's, and only because of the movie. To be honest, I probably would not have cared to see Avengers if not for Thor, as I thought Captain America was not that great, and never cared for Iron Man.
What i'm saying is the more familiar the GP is with multiple hero's in the DC universe, the better set-up WB can be for a JL release. This whole 2015 talk is sounding way to rushed for my liking, WB needs to take a step back and rethink there strategy if this 2015 JL talk is indeed their true interest.