Standard Jazz come on 15” steel or alloy wheels with 175/65 R15 tyres. There is no difference in the size of brake discs on EX models, so the standard wheels will fit. But an insurer will regard this as a 'modification' (even though, for winter tyres, it's a sensible one), so the change has to be disclosed. Sensible insurers will not penalise you for this, but idiot insurers do. If you use steel wheels you might need different wheel bolts.