15psi on the stock turbo? stock ecu as well?
personally i would f**k that shit boost controller youve got and get something that will hold the boost better. even the $30 one of ebay would do a better job than whatever youve got... ive got one and holds 11psi absolutly perfect.
also 15psi on stock turbo is gunna shag it, sooner rather than later, after 12psi they lose the efficiency anyway and it just gunna go on you. personally id set it to like 8psi min, 11 max. i had a turbosmart dual stage boost cotroller on my r33 when i got it, held boost fine. its for sale if you wanna make an offer.