I'd say yeah. That's not to say you can't do good with some 17", but I'm sure it's easier to achieve good mpg with the 15". The 15" have more "forgiving" ride, and cost significantly less. With 17" you have to work a little harder, lol. Both 15" rims and tires will weigh less, which also is good for mpg. Might actually be the main factor improving mpg.
Try this: Vrimz.com alloy wheel simulators Vrimz_Speedy_Wheels__Illusion-RS by citiprius posted Mar 9, 2018 at 7:29 PM
We had snow again yesterday, not much but waiting for good weather to clean the winter dirt off of the car and install my new wheels.