Yes, it does matter. Both a 13/65 and a 15/75 amount to a 5.00 ratio. But, the 13T will have better acceleration, and the 15T will have better top end. This is due to many factors, but weight of clutch drum, length of chain and chain slap, number of teeth engaged in the chain for drag, and some other physic beyond me, are all factors. I've found this to be true both in karts and bando's over the last 30 years.