I'm 15 too, and any educated doctor would know that a vegetarian or vegan diet can be acquired as long as the person consumes enough vital nutrients that their body needs. Eat lots of beans, lentils, whole grains instead of white, fruit, raw/steamed veggies, veggies cooked in a bit of olive oil, nut butter, raw almonds, oatmeal, smoothies, soy/almond milk, yogurt, hummus and even eggs, if you want (some vegetarians do eat eggs).
As long as you keep your diet varied and actually REPLACE the meat that would be in your meals with a high protein substitute, you'll be just fine! Don't only eat junky foods either, even if they are meatless. Be kind to your body. :)
Best of luck!