Are you looking for a smoother ride, or is handling and roadholding a greater priority? Given the same tire diameter (which you will want to maintain to keep speedometer calibration) the 15" wheels would have a taller aspect ratio tire, which rides softer, but also handles more vaguely than your lower aspect ratio 16" tires. Here is a good website to compare diameters and speedometer readings for different size tires: http://www.net-comber.com/tirecalc.html

Just FYI, the 15" wheels take 185/65 tires, but being 6" wide they'll easily accommodate 195/60 tires. Beyond that, you'll be getting the bulged out NASCAR look.