That's a good idea. If you've only been increasing by an average of 5 mpw per season, doubling that total from one season to the next is not a great idea.
First off, you should first consult with your coach on this (and every other question). That being said, for a high schooler your age/ability, I would start tempos after at least two weeks of easy running in base. Start with 10 minutes tempo and increase by 5 minutes every 2 weeks or so. Don't go to the well in base training. Finish feeling like you could have run another 5 minutes at that pace.
First of all, at your age (at any age really), it is not possible to build up your aerobic capacity enough. Building up your aerobic capacity slowly right now is going to help you more than anything else in the long run.
Some might say that you cannot run your base/easy mileage "too slow." I disagree with that sentiment. Too slow is when you are practically shuffling along with no concern for proper form. Remember, easy running, is still running and should be taken as seriously as any workout. For your easy runs, focus on maintaining good form, and controlling your breathing (this is where the term "conversational pace" comes into play). For you, I'd put that pace around 9:15-11:15 pace (based off 6:50 mile). Depending on how much fitness you have gained/how tired you are it may be faster/slower.