get a book on word problems. The one that I got was "How to solve word problems in Mathematics" by David Wayne, Ph.D. it helped me b/c on my DAT there were a lot of word problem.
you would also try this book its called "Secrets of mental math" I did a lot of calculation in my head. good book.
P.S. I made a 14 on QR but thats bc I had tuna salad. dont have that on your 15 min break. I was making 21-24 when I was taking practice tests.
Best of luck!