a friend bought a used 16" rim. i found out one was slightly lighter of about 100 gram or so.
will it caused the car to shake during high speed drive?

due to the narrower 195 width over the 205 and smaller diameter of 15", overall performance should increase.
ie; faster acceleration, more responsive braking and more comfortable ride( 45 to 55).
fc is very subjective; depending on the driving style and wheels' weight. some 15" rims are heavier than those lightweight 16".
and with better acceleration, we tend to put more pressure on the right pedal to feel the surge which is similar to pressing the accelerator harder on
bigger set of wheels to get the car moving. end result = no different in fc. unless cruising leisurely on the highway
another drawback; if the car's speedometer was calibrate on 16", changing to 15" will caused the speedometer reading to be inaccurate: -+ 10km/h.

looking for oz (prefer cosmic) 15" pcd 114.3 with 7jj. halfcut is fine.
any recommendation?