205 55 15 = 112.75(sidewall height, which is what determines how tall your tire is and how close your speedo will be......if the stock size is 195 60 15 = 117, then your gonna be about 4.25mm shorter than stock with the 205/55/15's on it......it will be off but maybe only 3-5mph.....if you are doing 60mph, it might read 65 or so.....i wouldnt worry about that.....no big deal.....