You forgot that a 35 on 17’s weighs more than a 35 on 15’s.
Of course, you're right, though I'm not sure what measurable difference it will make having 5lbs/corner more of unsprung weight. Aesthetics outweigh the weight penalty in my opinion. Of course, I'm running 35's on a 15" rim, but I do not prefer the look. One more thing to change.