Smaller wheels won’t necessarily be lighter. I just got wheels for my lanos and after tons and tons of research I found 16” wheel combo to be lighter than a 15” in the same size and wheel. This was because the 15” tire was approx 2 lbs heavier than the 16” tire and the 16” wheel was only approx 1 lb heavier than the 15” wheel.
You could probably still go with a lighter weight wheel. If your wheel is 17x7” or less there should be no reason to go over 20lbs for each wheel. 17s don’t have very many options for a really light, inexpensive, and good quality wheel. In 16” or less though check out the Rota Slipstreams, my 16x7” slipstreams weight 13.5-14lbs each…not sure on the weight as the newer production slipstreams got a tad heavier. I had 16x7 slipstreams in a rare color shipped to my door for only $520 recently.
Also performance BOLT ons don’t usually hurt fuel economy. I gained a couple mpg with my basic upgrades. Think about it. It still takes the same amount of power to make the car go forward. With performance upgrades you will get worst mileage when racing around than with a factory engine.