I hate to break it to you, but running long slow distance will not improve your 1.5 miler very effectively.
This guy is a strength and conditioning coach out of California who did several years in the Marines. His track sprint workouts contained there will vastly improve your conditioning and 1.5 miler time compared to running 3 slow miles multiple times per week. If you want to get fast in a short period of time, SPRINT. It sucks, but it will make the chaos of OCS that little bit less sucky if you've prepared. Run one long slow day per week at most, just to prepare your body for the impact.
I've incorporated these workouts into my normal regimen, and I've broken a 6-minute mile for the first time since playing soccer in high school, and I'm carrying about 30 pounds more in muscle.