Thanks for writing in this question. You’re not going to like the answer though. Like most things in life….IT DEPENDS. Now, I think I can make some assumptions based the comment about your 15hrs/week of training. You no doubt have developed a solid base.
By now you should know how much volume (vert/dist/time) you can handle in a week. There’s no way I can even come close to suggesting anything better than what you already now. It just depends on too many factors.
Now here’s the part yo might like:
Just doing more of the same; more vert, more distance and more time is not going to make you faster. Speed is directly related to leg power. My favorite ways to help develop more speed are though ME and Hill Sprints. Both of these will help increase you stride length and hence make you cover more ground for each stride. If you keep the same tempo, voila you go faster. These two workouts can be fit into the same week of training and should be done for at least 6-8 weeks in a row. You’ll get an even better effect when you in the 12 week range. Cycling through this type of training block several time over the course of a a couple of years, where overall trining volume will probably take a hit, will show nice results. I have some pros I work with who’ve been using the approach for as much as 6 years and are still seeing gains.
I hope this helps.