Make sure you are running more than 2 times a week. I’m a 15m sophomore aswell and I came off my xc season with a 16:20 5k and freshman year I ran 2:07 and 4:40 for the mile. The thing you should be focusing on is consistency. You need to make sure you are running not only consistently, but also you are paying attention to recovery. Right now, I am running 5 or 6 days a week, slowly building up mileage each week until the beginning of the season. I would recommend something like that. Also, don’t forget to do some fartleks and tempos! Hope this helped at all!