Not sure if this is your case aswell, but for me what's really helping is controlling my breathing. I basically practice in private for a few minutes a day, and it's helped more than any tips anyone has ever given me. As an almost-life-long stutterer I can see that I'm finally moving forward in my speech. (I'm 15 too BTW). Even with the breathing practice, however, you're right. Anxiety and a few other things also play a role in stuttering. The only tip I can give you there is to try and make yourself more confident when speaking. I bet you have cool things to say that people would love to hear! Just believe in yourself. Hope I helped you out.