what you score on practice tests doesn't dictate how you'll perform on the real DAT
before I took my DAT, I did 1 actual practice test (timed and all), I did so poorly in it, that I gave up doing practice tests cause they were demoralizing me. I only did thier questions / answers (from topscore and the free practice ADA test), I didn't time myself, and just did them like they were an exercise. I am not suggesting you do this method, I am just saying that what you get on practice tests many times has nothing to do with how you'll perform on test day
so getting a 15 or 23 shouldn't mean anything. Just do the questions, go over the ones you miss (so you can learn) and move on with your studies.
that DAT practice I took, If I remember I think I got an AA of 16, AND IT WASN'T EVEN A HARD TEST, it was one of the CD tests from the Barrons book.