what exercises and diets should I go on to achieve this.
right now my body fat composition is 15%
Aim for a more achievable goal first off. 10% Body fat is great for a male, and if you're going for a “cut” you'll be impressed with the results. Once you get below 10% it's much harder to lose the fat, but the method is the same:
1) Long and frequent moderately strenuous exercise – run, cycle, use an elliptical, etc. for 1 hr a day 4 days a week or more. Take a nice long warmup (10 minutes) then get your heart rate up to 75% of max and maintain it for 40 minutes or more. Make sure to hydrate – losing water weight isn't healthy at all! Cool down for 5 minutes at least, don't just stop.
2) On the days you aren't running / cycling do low weight high rep resistance or free weight exercises. A good barometer for weight level is you should be able to do about12-15 reps, and the last 2-3 should be a slight struggle. Do 3 sets – 15 reps, then 12 reps then 10 reps of each exercise. By the third set you shouldn't be able to do 10 reps…if you can, increase your weight by 5 lbs or so until you find the right weight. Make sure you are hitting all muscle groups – back, ab, shoulder, calf, quad, bicep, tricep, pec, etc. Don't rest more than 60 seconds in-between sets – by the end of the 45 min to 1 hr workout you should be out of breath.
3) DIET – you've got to virtually eliminate fat from your diet. Chips, candy, cookies, fatty steak, dark meat chicken, pork etc. have to go. Focus on fresh fruits and vegetables, plenty of carbs, and lots of water. Pay attention to your diet and you'll probably find a lot more fat going in than you think.
4) Tracking your diet and exercise – chart your self. Write down what you eat (no cheating) and how much you exercise. Stick to your game plan, and the fat will melt away really quickly.
5)REST – get lots of sleep, because your body needs it to maintain proper function. Exercise 6 days a week – rest one day. If you feel like you HAVE to exercise on that free day, only do 15 minutes or so, and keep it really leisurely. You can easily over-burden your system if you don't allow a day to re-set.
There are much more comprehensive and detailed methods out there, but that's the general game plan.
Good luck – hope that helps.