The connectors on the ends of the cables might fit into the ports. But beyond that, USB-C, as seen in the consumer space, is a hellstew of old and new standards. It is made up of a whole bunch of cables, chargers, power banks, and other accessories that "work" with USB-C but whose compliance with the standards is, shall we say, erratic.
I have to say, I'm not surprised. Apple's gone from using a tightly managed proprietary connector to one that, in theory, has stringent standards, but in reality is far from the case.
What's the solution here?
Apple either needs to improve the way the iPhone 15 detects items to charge or add a software toggle that controls which direction charge flows.
In the meantime, if you're affected by this, you could try different combinations of power banks and cables or maybe try flipping the cable around. I know it sounds weird, but while this is new to iPhone users, I have come across this in the past with some Android devices and certain combinations of charging hardware.