The only way therapy is a waste of time or money is if you don't give it your best effort. Don't worry about the outcome. Do the work. Doing something is always better than doing nothing. I had speech therapy in my teens. Didn't help. Because I didn't do the work. Went back in my 20s and got fluent. There's no guarantee speech therapy will help. Don't spend a lifetime wondering "what if I had tried speech therapy?"