M112 max boost

Hi guys, have been running an m112 on my 2.5 1jz for a while now at around 10ish psi. Now ready for around 20psi but i can't seem to any more than around 15?? Have a 3" nose and about 5.9" crank pulley, can I expect to get more than 15psi with this set up or am I probably Maxed out. Am not bleeding any boost off and it's a new charger. Engine is 2500 l6 redlining around 7k rpm, I can soon make a larger crank pulley but don't want to overspin the charger. Haven't properly checked for boost leaks but I'm fairly confident I havnt got any. Would appreciate any help or opinions if im being abit optimistic for 20 plus psi of if I'm missing something, just hoped I'd get more than this on a little 2.5L engine. Thanks guys