Why is charging taking so long?
The two basic rules are:
1. The charger always offers as much power as possible to the car.
2. It is always the car, that "decides" how much power it will take in.
If the car charges on a single phase, it will take 3,7 kW per hour. If the car is fitted with a 3-phased charger, it will take 11 or 22 kW per hour, depending on the battery state of the car and the power available at the charge location.
This is how to spot, if the cable is a single or a 3-phased cable:
A charger might be labelled "up to 22 kW", but it is always the car that decides how much power it wants. The desired speed depend on things like current SoC (State of Charge), battery temperature and cold or hot weather.
If there are several chargers on a location, the chargers will dynamically share the available power between them. If there are multiple cars plugged in, the amount of power the car gets can be low at the beginning; but will increase automatically, when the other connected vehicles are done charging.
Bonus info on Zaptec chargers:
ZapTec Go throttles from 50 degrees and when/if it reaches 70 degrees it cuts Amps down to 0.
ZapTec Pro throttles from 60 degrees and when/if it reaches 85 degrees it cuts Amps down to 0.