How best can a 220 pound 15-year-old lose 66 to 70 pounds?

First off, see a doctor, seriously, you need medical attention of you are that overweight at 15.

Secondly, it's really rather simple, EXERCISE! You should be doing around 5 hours a week, if not more in order to be able to eat 2000 calories a day without gaining weight, talking of which, restrict faithfully if you want to see results, avoid 'fatty' foods such as crisps, chocolate and fried foods and instead go for fruit, veg, lots of water and good carbs like brown rice and oats.