Schedule a checkup at the vet and ask them.15lbs/ week is crazy. My giant breed pup is an eating machine and can’t match that. I’d switch to whatever kibble your vet recommends, probably something like Purina pro plan. They can tell you how much kibble he needs too. I don’t think vets are big on people making their own dog food. They’ll usually push for kibble because it’s tested and proved to be a safe, complete diet.
I add a spoonful of canned pumpkin, plain yogurt, some boiled chicken or turkey, an egg or some carrots to my picky eater’s kibble to entice him to eat. Or I put his kibble in puzzle toys, the only way he’ll eat his food plain. It’s more work than you need to do though, I’ve created a brat and I’m okay with that. You can also just give your dog plain kibble and wait it out if your dog starts a hunger strike for yummier food. He’ll give in and eat what you give him within the day. Dogs really don’t need extras if they’re on a good kibble.