This original source does not say anything about what the phone will support. It is about the charging cable that is included.

It's just the charging cable, it seems it does not have all the wires to support USB 3.

The rumors and articles on this are all over the place. Some are reporting that the non-pro phones will only support USB 2.0 speeds while the pro phones will support faster Thunderbolt.

Others talk about the cables saying that Apple will ship USB-PD (power delivery) cables which are specified as USB 2.0 with all of the phones.

Are the speed limits on the ports or on the cables or both? When these launch there will confusion for several days and perhaps until testers get them in their hands to try different cables.

I imagine it’s just the chip. It would be really weird if features like (wired) Continuity Camera just stopped working.

This is only about the included charging cable. What the iPhone 15 itself will support remains to be seen.