From personal experience (having tried all three sizes - 15, 16, and 17), all tested with road approved race tyres:
15 and 16 - Had OEM EK9 wheels when I first started out, were great to learn on because they weren't too expensive if I wrecked one (about NZD150 for a crap set - yes, a set!
). The step up to 16 was interesting, the size was 16x7.5 (Advan RG) so were the same weight as OEM and the same OD so performance wasn't affected, but the wider tyre meant lots more grip, and braking performance was improved also.
I recently changed to a 17 (to fit over my new brake setup), and although the OD is slightly larger, the increase in braking performance and grip have more than made up for it, the car is now much faster than ever before, especially through corners.
During back to back testing with a transponder in the car using official timing, someone I met through racing circles who races an EG6 in the local Honda Challenge series found that a 17 was by far and away the fastest wheel, even though it weighed more. Tyre wear was greatly reduced too.
Up to you at the end of the day, if you like 17 inch wheels then keep them, although JDM purists might disagree!