Well, that really depends... it's good for alot more boost than that on a much smaller engine...
Say a geo metro engine, it'd be good for 20+ because the intake restrictions are so much larger.
If you put a t-25 on say, a c5 corvette, it probably wouldn't make a single pound of boost because the LT-1 can injest so much air!
See what I'm saying, here? Just because it'll make 13-15 pounds without a problem on the engine it comes off of, doesn't mean it'll make that much boost on all other engines. It has to do with AIRFLOW, not boost levels.