You're lucky it disappeared for 15 years. Mine has disappeared 3x in my life; once for 3 months, another for 6 weeks and most recently for 2 weeks. I'm 40 now and thinking about being fluent is like chasing the dragon. It's not good for me. Your situation might be different because you were fluent for 15 years and I hope it is. That being said, you need to take care of yourself. Go workout, get a haircut, eat right, get good sleep. It probably won't help with your stutter but it will help you feel better in general.