30 psi as compared to 15psi (taken completely literally) will cause no problems. An extra 15psi added onto the combustion pressure becomes almost a drop in the ocean. In pure pressure terms I don't think it's a problem.
You'd need to specify what turbo (and hence airflow) was being used to force the air through all the restrictions (in the engine/intake system) to cause this pressure rise. If you are talking about a big T78 or similar then the airflow will be huge. So by that arguement, once fuelling is correct, you're talking an awful lot of power for a stock engine.
I have no personal experience of 600bhp+ 2JZ's so can't comment. US "experience" suggests the motor will hang together but it's a potential time bomb. Stock gasket is about the best around I believe, not sure on head screw specifications so can't say.
I don't think you're asking this in the literal sense though, you are talking about the engine being capable of withstanding the loads generated from what would be an extremely high specific power output. Revs are the killer, stock bottom end certainly isn't a rev machine that's for sure. What sort of revs would you be talking about holding that boost to - stock rev limit wouldn't cut it with the necessary turbo and cams for that boost from a big turbo.
I think the pistons would be "ok" (assuming no det, nice chilly charge temps and adequate octane and afr). My major concern would be the conrods and the rod bolts - serious imposed loads there!
My 2p