The 6 kW onboard charger will fully charge a 24 kWh LEAF from dead in 4 to 5 hours (depending upon how much charge tapering and balancing is needed) if the EVSE can supply at least 28 amperes at 240 volts (at least 32 amperes if voltage is only 208). The car will not charge faster than this even if the EVSE is capable of higher current.
Gerry
Gerry