Well, if you have the money I would just get an ls and go turbo. I am personally putting on an IHI T3 on my D16 right now and i will run about 8lbs of boost and a 50 shot of spray. I don't see anything wrong with boosting a D15 expept they are not built with very strong internals. I am running just a 50 shot of spray and I need new piston rings already, but I have put probably 12 bottles through my engine.
If you want to boost the D15, I would say lower your compression, put forged pistons and rods in it and boost the hell out of it. The lower the compression the more boost you can run.
BTW. I have stock internals but I am still going to boost that. I have a friend with the same engine as I do and he runs 6psi of boost and has had the turbo for a year now. With no real problems.
Thats just my two cents.
-Chris