The best mod you can do righ tnow is to do a search
I'm running 1 bar on my stock turbo (14.7 psi) but I'm not afraid to let it blow... I'm saving for a new one and have one spare in the garage anyway... if you want to boost it up to 15 psi without an intercooler or an ECU, you will most likely blow your turbo. It's not even a matter of if, it's a matter of when, and you might get a month out of it at best...
Highly unadvisable