It's 12A. And the breaker will be at 15A. 12A is the max allowed for continuous on a 15A circuit (20% derate) and car charging is considered continuous use by code.
The breakers will not be rated for over 20A. It depends on the wire, but the outlets aren't rated for more than 15A usually, 20A tops and you cannot put a breaker higher than the outlet rating on a circuit in the US. In other countries like the UK where outlets are individually fused, you can have a high power "ring circuit" such as you speak of.
It is very easy to trip circuit breakers charging EVs off random outlets like this. This alone is a good reason for people not to charge off random outlets like this, think of the people inside who lose services because you tripped their breaker.