AFAIK for EV charging it is ~1400W for a 15A outlet and ~1900W for a 20A outlet (because the load is continuous), and the difference between the two for the Model 3 is probably around two miles per hour or so.
Correct, assuming a dedicated circuit in the US, code dictates that it'd be 1440W and 1920W for a 15A and 20A outlet, respectively. Continuous loads can only pull 80% of the max circuit load.
In theory, you could also run a 100% rated breaker to pull more power, but the car would have to be able to support it as well.
In theory, you could also run a 100% rated breaker to pull more power, but the car would have to be able to support it as well.