Originally, the 2011 units were upgraded to 120/240-volt operation, but remained limited to 12 amperes so they were fitted with L6-20 plugs. Upgrades of 2013 and 2014 units were fitted with L6-30 plugs because they were capable of a maximum of 20 amperes (adjustable down to 6 amperes in 1-amperes increments). Later upgrades of 2011 and 2012 units were also adjustable and capable of a maximum of 20 amperes so they were fitted with L6-30 plugs. 2015 through 2017 units are adjustable, but limited to a maximum of 16 amperes. Therefore, the 2015-2017 units could be fitted with L6-20 plugs, but it appears that EVSE Upgrade has standardized on L6-30 plugs so they only need to stock one size of plugs and adapters.
I am not sure when Nissan began adding temperature sensors to the plugs on their 120-volt EVSEs, but my 2015 has one. Therefore, it might be better to keep the EVSE that came with the car for charging on 120 volts only and obtain a used 2011 through 2014 unit to upgrade for 240 volts.
Several posts were added to the thread after I started typing last night that cover some of the information above, but I want to add that I have two EVSE Upgrade units and am very happy with them. I have an original 12-ampere 2011 upgrade which I purchased soon after complete units became available from EVSE Upgrade to keep at my workshop garage for faster charging there. After the crash, I took the original Nissan unit out of the 2011 because I did not want the body shop to charge the car and let it sit at full charge. I talked to a representative at EVSE Upgrade after getting the 2015 and decided to upgrade the 2011 unit to 20 amperes and keep the 2015 unit with its temperature sensor in the car (remains covered by Nissan warranty) for 120-volt charging. The 12-ampere maximum was fine with the 3 kW onboard charger in the 2011, but the 20-ampere maximum is much faster with the 6 kW charger in the 2015. I now keep the 12-ampere unit at home in case I ever need to charge from my portable generator.
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015