Need advice with senior

My now 15 year old dog has been on a raw diet and thriving since he was a puppy but lately he no longer has interest in raw food. I always rotate brands and proteins but he now seems reluctant to eat but will demolish treats abd . Ruled out any health problems at the vet so I’m assuming fresh raw is just too hard on his body digestion now. He’d rotate between such foods as Steve’s, WFR, Green Juju , Smallbatch and Stella and Chewys.

I switched him to Smallbatch lightly cooked and he seems to have interest in eating again. Any tips to make the raw food more palatable and easier on digestion (tried adding warm broth but didn’t help) or should I just accept that he can only do lightly cooked now?