Neither one holds up better under boost. The d15 has toothpick rods (moreso than a d16) and the y8 has a terrible oiling system as compared to the 88-95 blocks. IF the y8 doesnt spin a bearing itll make more power, but its almost guaranteed to take out the bottom end if you dont port/shim the oil pump at a minimum. On top of the y8 head having a fucked up cam timing setup.

Find yourself an older block and be happier.