actually for 15 psi thats not all that bad really. but you can push it a bit more even on 91 octane. can go to 17psi and keep the timing low if your still concerned. but getting a blower like that is a bit overkill unless you get it up to at least 17 to 19psi otherwise it wasnt money well spent, could have gone a bit cheaper and gotten the same results.
but hey, in the end if your happy and satisfied with the results thats all that matters
but hey, in the end if your happy and satisfied with the results thats all that matters