If you're relatively fit and find yourself concerned over fifteen pounds, there really isn't much of a concern there. Fifteen pounds isn't really enough to put your Body Mass Index (BMI) at a point that you should be worried. Clean up your diet (remove junk food); get a health dose of solid protein, good carbs (rice, potatoes, etc) and healthy fats (Olive Oil, almonds) into your system; if you're a sugar hound, choose stevia (Truvia). It's sweeter than sugar and has no calories.
Your boot routine is going to be largely calisthenic. To prep for that and balance that 15 pounds out I recommend doing circuits, a series of intense exercises that are conducted within time limit and then repeated after a short amount of rest. Try to hit all major muscle groups.
Example Circuit
I. Push Ups (Max amount in 1 minute)
15 seconds rest
II. Chin Ups (Max amount in 1 minute)
15 seconds rest
III. Crunches (Max amount in 1 minute)
15 seconds rest
IV. Deep Squats (Max amount in 1 minute)
15 seconds rest
V. High Step Run-in-Place (Knees up to waste, 1 minute)
Rest 2 minutes. Get some water, catch your breath, start it again. Repeat circuit 4-5 times. Five days a week.
This targets both your cardiovascular and muscular strength, mimicking military calisthenics. As your cardio fitness increases, the routine will get easier. When it does, start reducing/dropping rest periods; then start adding exercises to your circuit. Don't be afraid to be creative with the exercises you add. I've had pre-boot clients hold a twenty pound rock in various positions for one minute. It's not easy, but it works.
Hope this helps.
Cajunguy, NSCA-CPT (among other things)
