In theory it should be ok, if a little on the rich side. But to be honest i would leave it at 18psi and just drive it more gently if you're worried about it. You can fit a low boost switch too incase the 18psi is too much for wet conditions etc.

As long as you aren't a moron with it, it should last fine at 18psi, its a good solid power figure. I'll be having mine setup at around 20psi, and i've got low boost switch.