Will smaller rims make your car lower?
Depends on if the tire size is smaller too. Yes.
Putting smaller rims on your car will make it lower. You can use a car performance simulator to virtually try different rims + tire setup and see how this will affect performance. Low-profile tires are being offered for several reasons. Check out http://www.popularmechanics.com/cars/how-to/repair/should-you-put-low-profile-tires-on-your-new-car for more details.