16' inch is a odd size. If you see most UHP or performance tyres out there, not many models you can choose for 16'. And there is major price difference between 15 and 16. Might as well get 17' which you have more choices on better tyres.

Back to TS concern, since you have made your mind to change to 15', do you still prefer to more or less same FC? If yes then go for 185-55-15 for comfort and agile (lesser rolling resistance).

If you wanted more grip aka handling performance but sacrifice abit of FC then go for 195-50-15. 55 series tyres are much more expensive.

Better FC = Lighter right foot.

Want car to have good response and since you driving in city, go for 185-55-15