How can i lose belly fat? please help?

Hello, i am a 14 year old boy that is 5'5. I am currently around 155 pounds and i want to lose 15 pounds. Every day i watch what i eat, and i do 30 minutes on the elliptical, 20 bicep curls on each arm, 50 jumping jacks, 2 minutes on the plank, 50 situps, and 10 pushups. How long will it take me to reach 140 pounds if i continue at this rate?