I am surprised a Vet put a puppy on a therapeutic diet that is meant for older dogs with joint problems. Never heard of something like this. Sounds a bit odd. Unless there is a medical reason for this, take the dog off this diet and get your money back, all of it. I am sure Hills would be surprised that a diet like this was "prescribed" for a healthy puppy.
It doesn't meet any the established nutritional standards for puppies, and the established standards are extremely low.