Will Falconer, DVM Moderator
Nice work, Lori. He sounds like a rare example for his breed, though I've probably seen too narrow a sampling as a doctor.
I'd get a senior blood panel run at 15, just to see what's what with his organs. Then you'll have more room to make determinations of how he may need help. That, along with a consult with a homeopathic vet who goes over all of his symptoms would be the best prevention for a guy his age. Likely, with some probing, you'd find more than just sleeping extra time.