The difference between 15w and 22.5w charging treasure is that the charging speed is not the same.
The relative current will be proportional to the large power, and the large current will quickly charge the phone.
The current is like a cubic reservoir, you need to fill it with water, you use a 5 centimeter diameter pipe and a 10 centimeter diameter pipe, and obviously the 10 centimeter pipe will fill the reservoir faster than the 5 centimeter pipe.