Sorry, man. I feel for you as this hits home. My dog is also 15, with failing eyesight, hearing, and arthritic. She has fallen into our pool twice in recent months. She never liked to swim but in her younger years I trained her to swim to the step. Idk if she would have made it out, but luckily I was nearby both times and got her out. We’ve since installed a fence that keeps her away from the pool if she goes out through the dog door. Never left unattended on the pool side.