Is he for sure overweight though, or just a bigger Yorkie? Jackson's about 13lbs too but not overweight. It sounds like you're doing everything right- giving him lots of exercise, etc. Nature's Recipe is not a bad food, it's one of the better ones you will find at Petsmart. You can see
Dog Food Analysis - Reviews of kibble for more info. That particular food is rated 3 but the ingredients are not that bad to me, it probably could have a little more meat, but other than that, I don't see any red flags.
Dog Food FAQs: Frequently Asked Questions on Dog Weight Control
Here's a site with some pictures.