Well I guess you should do some training at 15k pace.....
Lots of ways to go about it. Short fast tempos (2-4mi at race pace)....mile repeats @ race pace with short recovery (8 x 1mi, 4 x 2mi)....also your typical faster mile repeats (5 x mile @ 8k pace)...typical shorter reps too (400s/800s)...extended longer hard runs etc.
Training is easy. We make it hard.
You have to race at X pace. You have to race at Y distance. So the majority of your workouts should be running at X pace.
I would do a weekly workout that is at X pace, and a weekly workout that is either faster than that pace (see traditional mile repeats or faster track work) OR slower but at Y distance (8-10mi uptempo). Also your X pace workouts should be on the road.
Take it all with a grain of salt. I just try to apply common sense.
Alan