Took my 13 GT, SGM, with M6, 55D and 401A, to the dealer for service and noticed that they had a couple 2015 Mustangs on the lot. One was an EcoBoost and the other was a GT Premium.
The seats in the 15 felt like the old Recaros that were in my Indy Pace Car that I had many years ago. The motor sounded very nice and somewhat "raspy" (you had to hear it), the M6 shifted smoothly, and the car felt very tight. Never went above 60mph with it as it had under 20 miles on the car. Brakes felt very balanced... compares to my VW Jetta TDI. I shifted at less than 3 grand as the car isn't mine to pounce on but it ran very well.
If I didn't have my car, I would have bought this one on the spot. I know... it's a "lesser" car per se (power, braking, and options) but it was nicely balanced and optioned for what I needed.
The dealer asks me about my car, what I owe on it, how much I think it's worth, and so on. I gave him my info and invited to check out my car (wow, it's really clean!) and to get a hold of me at a later date.
I get back in my car and drive it the same way I test drove the 15... I really like my 13 a lot! Good thing I didn't test drive the '15 GT...