Is there a good tune out there for the 2015 Vanquish?

I'm hesitant to mess with Exhaust and headers, as I don't want to touch that sound, but I have to believe that motor is able to make more power with a good computer tune up.

 

Indeed it is. There's still some ceiling in the new VVT Controlled V12 Bosch engines. Same fundamental setup as the GT12 and that has a fair bit more power, a lot of it is torque limiters. There are no OBDII available protocols, but we do bench tuning for these here in Canada, had 4 of them in just the other day: