It's understandable that you're concerned about your stuttering. There are different types of stuttering, and it's important to understand which type you might have. Most of us are developmental stutterers, but you don't fall under this category it would seem. So, I suggest doing some research on psychogenic stuttering, and neurogenic stuttering to see which one resonates with your experience. If you only stutter for the last 3 months it's likely psychogenic stuttering that has a very high recovery rate. Or, if at age 15 brain damage caused stuttering, then it might be neurogenic and if so it's always a good idea to speak with a healthcare professional, such as a speech therapist or a neurologist, who can help diagnose and guide you in finding appropriate treatment options. My best advice in my opinion is to not pay attention to stuttering and not care about speech errors to prevent developing a habit of anticipating stuttering and to not add tricks to improve fluency (like timing your breath and articulation). Instead, put complete faith in the feedforward system and reinforce spontaneous natural speech and always stay calm and breathe calmly regardless of self-doubt in your ability to speak or fear of negative listeners responses. Because I argue that this advice could prevent developing elements of advanced stuttering and likely increase the chance to naturally or spontaneously recover from stuttering