Wheels, stick with 15s or move up to 17s?

No, noticeably rougher. Tires have cushioning, wheels are solid, if you trade 2 inches of cushioning for 2 inches of solid, ride comfort will decrease. Handling may improve, looks may be different, but comfort will decrease.

 

I upgraded to 17" wheels about 2 months ago and the ride got much stiffer and louder, especially noticeable on the highway. I also lost a few MPG, but hey, I really like the look.

 

I don't think anybody gets 17" wheels to make the ride smoother. It's mainly for the look, as well as improved handling.

 

Most of your ride quality/noise come from your tires, not just wheels. I upgraded to 205/50/17, the ride didn't change nor did it have noise increase. I used Hankook Ventus V12 summer tires on TC wheels

 

There are a lot more tire choices (for comfort, LRR, etc..) with 15" rims.

 

I was going to upgrade to 17s but then I found the 15s are actually alloys with a plastic cover on them. I pulled off the cover and got center caps from Toyota and they look great plus the 15s get better mpg. You can see pictures of with and without the plastic covers in my photos.

 

The 17's look really nice but between the cost to upgrade wheels and tires and the loss of around 2 mpg it is not worth it to me.

If it is something you want to do to your Prius then go for it.

Like I said the 17" wheel and tire combo really does look nice on the Prius.

 

I am on the fence on getting 17s. A part of me really wants them for the looks and handling. But, I don't want to fork out the money when the wheels and tires are doing the job fine. Maybe when it is time to replace the tires I will upgrade.

 

I may get 17" rims when I need to buy 4 new tires, I've been doing research and looking on ebay ahead of time - but I'm not about to spend money where I don't have to.

I'm all for functional mods.

 

I went with the 17s, albeit the 17s from a Scion tc. I like the look of the bigger tires on the Prius (it does fill up the wheel well a lot better than the stock 15s), and the handling is vastly improved. However, you should take into account:
1. Ride will be a lot harsher. That's the tradeoff for better handling.
2. Your mileage will suffer. I dropped anywhere from 4-6 MPGs, and that's with me concentrating on driving more efficiently.
3. Your acceleration, off the line and at speed, will suffer dramatically. Not that the Prius can do burnouts off the line, but it definitely loses the "pep" when the accelerator is mashed.
For the record, I swapped back to the stock 15s. Yes, I can't push the Prius around corners like I would with the 17s, but I think the 15s actually make the Prius more fun to drive (at least more responsive to acceleration inputs). I think the best compromise would be a set of light 16s with LRR tires.

 

I did upgrade to 16inch "very light" wheels. They weight less than original 15inch wheels.

And installed 15inch wheels to winter tires.

There is small problem with offset. Prius offset with 15inch wheels is different than Prius with factory setup 17inch.

 

17" are wider, they are very close, nothing to worry about