There's really no way of saying for sure. Every test is scaled differently so the requirements for different subscores are all different.
The best way to get an idea of the scoring though is to look at the practice AAMCs.
Log into
www.e-mcat.com and look for the link on the left "Understanding Scores" (I can't link cause you have to be logged in).
Compare it across the different tests..
Verbal score of 10:
-11
-9
-10
-9
-10
-10
-9
-11
so it looks like you can get around 9-11 wrong and have a chance at a 10. Of course, your test may vary but it's likely to be around here as we have a bunch of data points here.
So.. 1.5 a passage wrong is probably around a 10.
The MCAT is not curved, it's scaled. There's a major difference.