You may race year round, but bear in mind there are races and then there are "races". You'll want to choose a period of time that you want to focus on, even though you may race year round. For instance, there was a great series of summer and winter all comer meets that fit in between our fall cross country season and spring track season. Most of the people in my area would run some of the all comer meets during our off season just for fun. For us, it was a nice fun way to throw some more intense stimuli in the long months of base training.
Figure out the times of year where the races are less important. Those will serve as your "base" periods. The times of year where races are important should serve as your "competition seasons".
During your base period, you should work on things such as increasing your overall tolerance to training by increasing your volume, doing lots of auxillary exercises: drills, stretching, calestenics, plyometerics, weights, etc. Work on your sprint speed a little bit during these periods as well. If your club has a good sprint coach, get some help once a week from him or her. Any quality workouts you do can be done at "easy tempo" pace or "tempo" pace. Maybe once every 2-3 week touch on tinman's CV pace.
Think about your training like this: Your workouts are either going to be designed to build capacity, maintain capacity, or recover. If you're not tied down to a calendar too closely, you can try to touch each one of those bases every 3 days. During your base, a 6 day period might look like:
Build: Long run with strides incorporated toward the end
Recover: 30 minute easy shake out run, drills, stretching
Maintain: 40-60 minute easy - moderate + Calestenics or weights
Build: warm up + 30 minute "easy tempo" or 20-25 min worth of tempo intervals with 1 min rest + 4 x 200 @ 800-1500 goal race pace with full recovery.
Recovery: Day off, or easy 30 minutes, or some sort of cross training (bike, swim, soccer, etc...)
Maintain: 40-60 minutes easy + 3 x 30m fly in sprints.
Depending on what you're really trying to build, your next day in the cycle could be another long run, but for a 15 year old, maybe it should be another easy tempo or fartlek, or something like that.
When you get into your competition season where races are more important, you need to build your schedule around them. They should be the main effort for that training block and the other stuff you do should be designed to support your racing. It could look something like this
Build: Race 1500m and 800m
Recover: 30 minute shake out
Maintain: 30 minutes easy run + 6 x 300 at 1500m race pace, with 100m walk recovery
Build: 3 x 5 minutes tempo interval + 3 x 600 @ 3k pace with 200m recovery jog.
Recover: Bike ride, other cross training, or easy jog, or complete day off
Recover: 30 minutes easy run + 6 x 200m at 1500 race pace with full recovery
Build: Race 3k