A quick Google search reveals that Connecticut has cheap electricity rates, so use whatever charging rate you prefer and don't worry about the efficiency.
It's pretty hard to justify the expenditure for an L2 EVSE, if your only consideration is saving money because buying and installing the L2 EVSE will cost you at least $1000.
At $0.10 per kWh, if you assume that L1 charging is 20% more efficient than L2 charging, then you would save $0.02 per kWh. So, after 50,000 kWhs of charging at L2, you would finally break even on the L2 EVSE (or roughly after 2500 full charges on your LEAF).
The main reason to charge at L2 is for convenience, which for me is worth the expense
Vancouver, CA owner of a 2013 Ocean Blue SV + QC, purchased 01/2017 in WA
Zencar 12/20/24/30A L1/L2 portable EVSE
1-1/4" Curt #11396 hitch
After market, DIY LED DRLs
LeafSpy Pro + Konnwei KW902 ELM327 BT OBDII dongle
Loving my first BEV