As long as the outside diameter of the wheel doesn't exceed the original, you'll be fine. There is no doubt that the 15's will ride better and there are more tire options available. The slightly shorter sidewalls will improve cornering. I did this on my Bimmer E30 and the improvement was dramatic!
Fernando, your car has wheel covers. So that means that your 15" rims are steel, correct? Wouldn't those be less expensive than bundt alloys and easier to find used? I like the look of the wheel covers better than the bundts but that is personal preference. The bundt wheel would be lighter by several pounds per rim and that would make a difference in shock performance.