Tea? As in black or any other caffeinated tea?
I'm personally not very pro-cutting meal portions, specially if the diet you're giving is not nutrient packed. What you will achieve instead is a dog that is not getting enough nutrients, while most of his calories come from invaluable sources like corn, by products, and other fillers.
From the food you're giving, top 10 listed ingredients are:
Chicken By-Product Meal, Brewers Rice, Wheat, Corn Gluten Meal, Chicken Fat, Corn, Brown Rice, Natural Flavors, Dried Plain Beet Pulp, Wheat Gluten.
None of this is a plain muscle tissue animal source. The following ingredients before salt (1% rule of thumb) are vegetable oil, some tomato paste, fish oil and fillers.
So the problem here is what you're feeding, not how much. Your dog won't digest most of this ingredients very well, and they will store as fat.
When it comes to treats, low fat ones aren't necessarily best unless prescribed by a vet, and they can make more harm than good. Dogs, specially older ones, need all the good fatty acids they can get. I'd say give your dog meat based, low calorie treats like the Merrick chewy bite ones (I think they go 3 cal each), plain pieces of turkey/chicken deli (no salt) or whatever meat you have handy, or dehydrated meat that is just meat.
In terms of diet, I'd say it's a good idea to change the actual food to something that contains more lean meats, organs, fats and some fresh veg/fruit and less fillers or grains.
As in what you have now, I'd say try giving your dog half an egg, some plain chicken, maybe some veggies (a little, less than a cup) and a quarter of kibble. You should be able to watch the fat melt off. If you want quick results, go full home made, but they won't last if you go back to the old kibble.
Like all diets, they are a temporary solution to a lifestyle problem.
