I am driven (No pun intended) by current F90 ownership and 1 rental day experience where I got to experience 2012 R8 V10 spider and hated it and actually liked my F10 that I had back then, way more, and then I upgraded same day (Actually within one hour) to the most beautiful car I have ever driven R8 V10 2017 in RED with Formula 1 exhaust (So I was told), and it was light years ahead of my F10 which was Comp and had the Akra exhaust, and I loved that Audi 2017 and yes it beats my F90 in every respect bar none! Maybe maybe except the very obvious being PRACTICALITY!
If you want me to spell it out how F90 will be better than your Audi R8 2015, IMHO Steering, speed, tech, sound if modded right, dramatic mods impact, maintenance, creature comforts! Except handling and exotic bragging rights
So in a nutshell you'll love the F90 Comp but mod it heavily and right and get an exotic color!
If you had the Gen2 R8 I would have told you don't do it but 2015 not even a fair comparison, and I agree with Vic55 it's apples to oranges!
My 2 cents