Give it time man. Since you're still pretty young it could take some time. I was way more of a track guy in HS too, I only ran 17:05 for 5k in high school during xc, but on the track ran 51 (4x4), 2:01 and 4:38.
When I got to college I did higher mileage and a lot more strength stuff and ended up running 50.1 for the 400 (4x4), 1:54 for the 800, 3:58 for the 1500 and 14:57 for 5k on the track this past spring for my senior year. I went from 28:48 for 8k in xc my freshman year to 25:21 my senior year. Doing higher mileage in college allowed my track speed to translate to endurance and strength, therefore giving me a much better range from 400 to 5k.
With a 4:24 mile PR, I think you could go near the 16 flat barrier by the end of the season for sure. It's also not even October yet, so it's still plenty early.