13 Y.O. Jack Russell Terrier and Dry Kibble

Hello everyone, I have a 13 y.o. JRT that is in good health, not over weight, he is not very active. Because of large dogs that run loose in the neighborhood he does not get taken for walks, he is a indoor dog and has been since we got him as a rescue when he was five.
He was on Eagle brand lamb kibble from when we got him until about 6 months ago because the local pet stores stopped carrying the Eagle brand. I switched him over to Taste of the Wild Sierra, he will sometimes leave food in his food dish, more so than he did with the Eagle brand. He has gas and smaller and less well formed stools compared to when he was on the Eagle brand. He is constantly chewing his feet and licking since he has been on the Taste of the Wild food and he does this much more than when he was on the Eagle brand.
Should I give him more time to get used to the Taste of the Wild food as it is supposedly a better kibble or should I change him over to something like Orijen’s Senior kibble?
Thanks in advance for any advice offered.