Don't know about performance but there is quite a bit on rpm's. Going from the 15 to the 19 the rpm will be reduce around 800 rpm. The reverse will happen if you go from a 19 pitch to a 15 pitch, the rpm will increase by 800 rpm
The diameter does make a difference but both would need to be the same pitch and diameter. To compare the two with that much pitch difference would not be noticed
