If you maintain the same tire diameter is shortens your sidewall, making the ride more rough, but cornering will be more responsive. If you switch, it will be a noticeable difference. As far as being uncomfortable? That is really subjective and still will depend on how the rest of the suspension is setup. Assuming everything is stock and switching to 17's with the stock diameter wheels, I personally would think it is still a livable ride for a daily driver. But, I really hate driving cars with a plush ride.
In words, if I say stock 15's are a 10 as far as ride quality, you might drop to a 7 going to 17's. That is my opinion.
This is just going to be a very hard question to answer with words.
To add to the issue, if you can widen the tire at the same time, you can smooth out some of the bumps.
