Hi Elizabeth-
Regarding the weight issue…26lbs to around 15 is a pretty big jump. I would start slow like you said and feed for 20lbs, then re-weigh him to see the progress. Once he hits 20lbs feed for 15. After that you simply would feed to maintain 15 lbs.
Also I would suggest using this tool, as it takes activity level into account: /dog-feeding-tips/dog-food-calculator/
I find it to be much more accurate than the bag, though both are still just a guideline.
Yes, 3 calories is very low for a treat, however it makes a difference how many he’s getting daily. It is easy to assume that you can overfeed a 3 calorie treat and it won’t make much of a difference, but over time it does. Is there any particular reason they need treats? If not, I would eliminate them and reward with pets and praise. Both work just as well as a treat.
