As posted, at 14.5, you are right about there from a time frame perspective.
Have you given the dog glucosamine yet? That allowed my lab about 10 more months of life, and without joint pain. If you haven't done that, look into it!
I had to put my cat down about a year and a half ago. She told me it was time. Jumped up onto my lap and just looked at me. She was very thin and the glucosamine wasn't working so much anymore for her. The process was good for her. She drifted to sleep while I was there holding onto her.
When I had to say goodbye to my lab, her spirit was still strong, but the body had given out. She couldn't stand anymore and while she did still like her pettings, if you petted her joints she would nip at you. Nothing vicious, but you could tell how much pain she was in. Process was good for her as well.
And this stinks. It really really does. No way around it either. But it is what you sign up for when you allow a pet into your heart. In many ways we treat our pets better than we treat our seniors when it is "that" time.