I recently acquired a new 2015 CT, and spec-ed a downgrade to 16" on the basis of the many reviews I read. Consensus seems to be ride is better on the post-facelift ones, better still on 16" wheels, but still not on par with the class leaders.
FWIW, I think the ride's pretty good on mine, so would recommend the downgrade to 16". It's certainly better than my old 2011 Prius ever was.
17" wheels on cars of this size are absurd.