Okay, this was a long time ago, but when I got out of college, I'd run 18:15 for 5k. I didn't run track my senior year, but trained for my first marathon instead (running 2:56). I spent the next year running distance (Pfitzinger's plan, an early version) and got my marathon down to 2:52 (and a half in 1:19) and then we moved. By then I had run a 17:50 on a fast course.
I met a new group of women and joined their club, and they were doing xc, so I switched from marathon training to xc. We did a mix of long intervals on grass, tempo runs, drills, weight training and I kept my mileage up around 70. I ran okay in xc. I did a lot of hill repeats, bounding and drills and road tempo and long intervals in the winter and only one indoor race.
In my first track race, I ran a 9:55 3k, which was a huge PR. In my first 5k, I broke 17 easily and kept lowering my times.
I think the big base of mileage I had helped and then adding the drills, strength work and intervals helped so much. We typically did drills on Mondays (easy run day), Tuesday (hard - intervals, hills), Thursday (tempo), and Sunday long. We occasionally would have a short speed workout on Sat. I lifted twice a week and we repeated the drills on both Tues and Thursday.
I think you'll be under 17 before long!