It's a no brainer IMO. Wait for the 2015. If you like it, buy it. If not there will be plenty of '11-'14's around to get at any time. I also agree that waiting for the 2016's might be a better move. After all the trouble the 2011's had at initial release, there is likely to be some issues with the 2015, as with all new models.
That being said, I didn't heed my own advice. I bought a 2011 when they first came out. I couldn't help myself with the 5.0. Mine was delayed shipping for 2 months, but I've not had a problem since delivery. Many others can't say the same.
2011 GT Premium 6M convertible. Sterling Gray w/401A package, charcoal seats w/grabber blue stripe. Security package. Roush front fascia, splitter and rear wing. Black bullit wheels with 18x9 front, 18x10 rear. FRPP suspension. FRPP x-pipe. Roush axle-back exhaust w/square tips. JLT carbon fiber CAI with custom tune. Carbon fiber engine cover & coil pack covers.