55 would fit and would be better in the winter as well, but won't improve the performance in any way and it won't be wider either. You need 205/50R15 if you want to go wider, but I wouldn't as 195 is wide enough for these cars in my opinion.
55 is the profile (height) of the tyre. It'll offer less performance as there will be more flex in the corners which will give you less confidence when pushing it properly.
If you are playing about with the appearance try spacers first before going to the cost of buying tyres. GT's in particular don't like certain offsets or tyre widths on the driver side rear corner.