2014/5 MPH

All the Gen 3 prius have a top speed of 115 MPH. Did you mean MPG?.

There are minor hits for more weight (sun roof?) and 17 inch wheels, but those would be true in any car. The less options, the better gas mileage because you don't have to carry them around. Unless you spend a ton of money, larger wheels are heavier than smaller wheels. (the buzzword for light wheels is forged, be sitting down when you check pricing)

 

6% - 7% BETTER gas mileage is achieved with the smaller wheels (15"). More tire sidewall = smoother ride. The expense of replacing the tires is also considerably less with the smaller wheels (15").

The handling is better with the 17" but if you drive on bombed out roads you'll like the 15" better. The 17" ride a little stiffer and corner better. Are you driving on the highway, or twisty, smooth country roads or through potholes?

 

We have two 2010 Prius'. The basic model gets much better fuel mileage that the 5 trim level. I don't know if the bigger wheels are heavier, since they are aluminum. The extra electronics etc. in the level 5 add some weight as, well and reduce carrying capacity.