If you are applying in the Midwest, 15 is way too many. Most people will tell you 5 to 9 and that's plenty, even if you are applying to competitive programs. I did about 12 in the Midwest, got interviews almost everywhere, cancelled a few, and felt like that was still more than I needed. If you are applying in the east or in California, you will want to do more than 10, but I don't know how necessary it would be to apply to more.
Check to see which programs guarantee you a spot in a prelim program, becasue then you don't have to interview there for prelim.
Now, with a great Step 1 (for neuro, it's really really good), but so-so clinical grades, your letters of rec will be important. But realisitically, you will at least get interviews at almost all if not all programs you apply to based solely on your Step 1.