I dont know what to do
This comment suggests to me that you should wait. If you're not sure, then the '15 doesn't seem like it was much of an improvement to me. To me, buying a new performance car should be based on whether it blows your mind. And if it blows your mind, it doesn't matter what anyone else says, you just know that you need it in your life. I would wait to see if whatever is released above the GT blows your mind.