there's a section for the 2015 mustang
since the car hasn't hit aftermarket locations yet, exhaust systems won't be made for a little while. best thing you can do is take your car to an exhaust shop and have them make you an exhaust. my suggestion would be a 3" cat-back system with no resonator and no muffler with 4 inch tip. I had an exhaust shop weld a set for my 14 gt and I love the sound. it also cost me the same price of an aftermarket axleback.
but if you want to wait, that's an option too
2014 Ruby Red GT A6 - 3" Magnaflow Quad tip Catback