Oil content in food

Does an increase is oil % in a dogs food really make much difference to a dog who has to stay on a low fat diet. What actually puts the weight on? So from going to a 15% from a 7.5% oil content is it such a huge difference?
Silly question i know. Obviously taking into account exercise & quantity.
Thanks

why does your dog need to stay on a low fat diet? Is it just to prevent him/her from putting on weight? I think you need to look at feeding amounts too. I had a very overweight rescue BC here (40 kilos!) and I never put him on the "light" food, I just fed him according to my vets instructions which were to give him the right amount of food for the weight he should be (not the weight he was) and then as he got closer to that weight gradually adjust it to suit his requirements. If your dog has to be on a low fat diet for health reasons then you would really need to ask your vet but if it is just to keep the weight off you could just feed less. Recommended amounts are usually too high anyway