Going the other way from stock 15" to 17" is also physically possible, but there might be some variations in suspension/steering and who knows what: the 17" stock vehicles may have some beefing up? On 3rd gen at least, the turning radius was greater on the 17" (lotsa fun trying to get into a tight parking space), the steering turn lock-to-lock is different, maybe some suspension tweaks too? That said, lots of owners do that as well, seem ok, lol.
Did someone say recently that the 17" Gen 4s have a different steering ratio, and different Power Steering settings from those with 15"? Maybe a GOOGLE search might find it? I just found this (re 2016 cars) Rough Road Area Spec cars have different steering ratio (13.2 vs 13.4). And depending on model, there is a difference in steering ratio. The Turning Diameter is different too - but then, it could be just the tyre width causing that.
Oh woops. Yeah, so what I was saying about going 15" to 17" applies: it's physically possible, and very likely fine. Still, Toyota may have tweaked the suspension/steering for the stock 17" models, which kinda begs the question: are the tweaks (if they still exist) trivial, or more important. Droves have done the 15" to 17" switch, survived.
No. Our 2010 Touring turns like the Queen Mary, with both the 17" OEM and the 15" snow tires. Try as I might, I always end up slightly diagonal in perpendicular parking spots.
I believe the overall wheels have the same outside diameter with just different sidewalk heights. That would give the 17” a harsher ride.
