on this the 14" 27.6" and the 15" is 27" so your speed will read 1.8% slower
or 58.9 MPH at 60 MPH than your old wheels, or 8.3% faster than stock size wheels and tires or you will be going 65 MPH when your speedometer is reading 60 MPH, here is a fun tire calculator to play with http://www.rimsntires.com/specs.jsp