205 is 205 no matter if it's 205/50x15" or 205/40x17", but the bigger question is which weighs more?

Usually 17" tires and wheels weigh more than 15" tires and wheels. And the heavier the wheel/tire the more power it takes to turn it. I think Sport Compact Car said that for every pound of wheel/tire weight that equals 9-10lbs static body weight.

I had a 17" wheel package back in the day and it was 45lbs. I have a 15x7" Enkei RPF1 with Azenis that weighs in at 32lbs. So right there that's 13lbs I lost of wheel/tire.

this would be 13*10=130lbs and that's just for one CORNER! 130*4=520lbs.

Pretty significant. And actually tire flex is good on front wheel drive cars. Too stiff a sidewall can make the tire skip across the road while cornering.