So sorry. It is very difficult. Your situation sounds similar to ours with our boy who was 15.5. We used a room to make an “assisted living space” for him with tile floor and a nearby outside door. I have used a “quality of life” scale for him and other dogs at the end to try to make the decision for the dog’s benefit, not mine. Here is one link. (https://www.aplb.org/resources/quality-of-life_scale.html)