Winter tyres vs. summer time consumption

Hello, I just Googled a bit and looked in the fuel monitor, but without clear knowledge. Drive the V50 1.6l petrol now since 3000 km and have found that the only way to stay under 7 l is not to drive faster than speed 100. I drive almost only motorway, always swim with, without much gas/brake. At the moment I have vredestein snowtrac winter tires on it. My hope to save at least 0.5 l / 100km: Does your consumption highway with same driving mode with summer tires? Thank you and greeting Elchtest