Since your XC season just finished take a break first. As I coach in the southern hemisphere I will give you a little of my experience in coaching a 15 year old who just ran 1:59/4:10 1500m in two consecutive weekends. Another 15 year old following this program just ran 9:13 for 3k (9:50 3200m)
So after XC he took 2 weeks off (to travel to Italy) then he came back with 4 weeks of good training to achieve these times. An example week:
Monday 5x3 minutes at 5-10k pace w/ 90 seconds rest 5x100m with 100m walk
Tuesday Rowing
Wednesday 30-35 minute run
Thursday 4x800m run as 400 at 3k pace 200m in 46 200m how you feel ( he averaged 2:32) 21/2 min recovery 4x150 accelerations
Friday OFF
Saturday 9k over hilly course
Sunday 50-60 minutes easy
Don't follow program but just an example week. Good luck