It depends on what Leaf you drove. If it's a S model without the charge package you won't gain a thing, it maxes out at 12a @ 120v, if it does have the charger package or is anything other than a S model, you could get double the charge speed using an EVSE that will go up to 24a @ 120v. Of course if you could get the outlet rewired for 240v you could get double the charging speed again or 4x what you currently get. Note a S model without the charger package will max out at 16a @ 240v.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a