Puppy isn’t finishing meals/gets distracted

Hi everyone, last week I brought home a 15 week old Shiba Inu puppy. Hes doing great so far but I am having some trouble getting him to be interested in his food. I was given a large bag of Health Extension little bites food along with a few cans of the same brand and was told that was what he was already eating. I currently give him 1/4 cup of the kibble with 1/4 cup of the wet food and I add in hot water to warm up the wet food thats been in the fridge. He gets this 2x a day plus I leave him in his play pen with a 1/2 cup of the plain kibble while Im at work (Im super worried about hypoglycema). By the time I get home from work he has eaten most of the kibble throughout the day however morning and night when I feed his "big" meals he will only eat part of it then get distracted and refuse to finish it even when redirected back to his bowl. How can I get him to settle and eat? Ive already reduced the portion I was giving him after assuming I was giving him too much but he still wont finish it. I also wanted to ask about the food brand as well because I was under the impression that grain free dog food has been linked to heart disease? Is there something thats better I can slowly switch him to? I'd like to add that I do prefer not to order his food online if possible if thats something worth noting. Thank you all so much in advance Im already learning so much on this subreddit!