You are correct. I get around 1.70 kw per hour on my 120v/20a versus 1.22 on the 120v/15a. So it would save me about 2 hours of the 12 hours if I were charging from empty.
Please note that the charger that came with the car will not charge at the higher rate. You would have to have a charge cord that would accept the increased amps.
I have a free ChargePoint station across from my work and that is where I do the bulk of my charging so I opted to not install a Level 2 charger at home. I still needed a much longer level 1 cord to reach across my garage so I bought one that was rated to accept the higher amperage.
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