KYDAD2023,
From spending time in the HitTrax machine (and watching the younger coaches jostle to hit with our 13u kids' drop 5/1.15 bats), the difference in exit velo is 10 - 15 % faster for 1.15 bats off live batting practice. I'm guessing exit velo with 1.15 bats is also 10% faster off the tee.