Just to add to the accurate comments so far, note that the stock wheels are very lightweight compared to the average 15X6.5 alloy, and of course the smaller tires will have much less weight as well. Compared to stock, your unsprung weight ratio is very high, causing poor inertial response of the suspension. In addition, there can be problems with the soft front bushings handling the stresses imposed by the wider, stiffer tire arrangement.

Steve