So, this is your first swap, your first SR20DET, and you're convinced that they suck? Thats funny. Your 15.6 is the slowest time I've ever heard from anyone running even a bone stock SR in a 240sx. I have heard of some 15.0-15.2 times, however.
When I drive a stock SR I find it quite laughable myself... but with a few bolt ons you can make 250rwhp no problem. It's not 165rwhp stock, its ~185. But hey, you've swapped one, so you must know now!
And who's to say that the motor you got isn't a total POS? I've seen some ratty SR20DET's coming out of junkyards around here in Okinawa, Japan. They ship a lot of crap over there. The difference between a motor thats been beaten senseless and one in nice shape is a lot.
To the guy talking about the only fast SR's being built... heh heh. Yeah, mine is 100% stock internals making over 400rwhp. It even has a stock headgasket. Last dyno was 395rwhp, 362ft/lbs of torque. I assure you, this one is fast.
Oh, and the reason why RB20DET's are so cheap is that nobody wants them over here.

I've sure never seen a fast RB20DET that didn't have $10,000 in it.