James, at 15, you really need to be thinking about providing your GROWING body w/ the proper nutrients from a balanced diet. This is your opportunity to set yourself up for your later years...you've got more natural testosterone running through you now than you will at any other time in your life...use it to your advantage! You're lifting weights and building muscle, w/ proper nutrition you will add & keep that muscle more easily than you will when you're older! Now is not a time to be going on a diet to get abs!
Why don't you post a typical days diet. I bet it could be cleaned up a bit, which will help you gain muscle and harden your physique, and possibly get you visible abs. Restricting calories and eliminating meals isn't the way to go though!