15w wireless charging is not fast.
His fast charge power is 18 watts, not 15 watts 18~25 or 22 watts, belongs to the power of the pd fast charge protocol, and 15 watts and 5 watts should be no difference, Apple has a charge protection chip, for some high power it will be reduced to 5 volts a amp can not be accepted, so the charging speed may be the same as 5 watts.