a 195/50r15 is @ the same as stock in diameter, a 205/50r16 is 1 1/2" too large, and is a 1/10" larger than the 18" wheel/tire that people are running around with. you should try a 215/40r16 it will have more sidewall that a 205/40r16 and still be in range, but you might rub because of the width.

you cant get bigger rims and keep the same sidewall. however lower profile tires have better reinforced sidewalls than the cheap oem tires that come on the aveo.