No, Apple didn’t change the Lightning connector on the iPhone 15 to make more money selling you new cables and dongles. It’s a common conspiracy theory that Apple switches the connector all the time for lining their pockets, but it doesn’t hold up to scrutiny.
First of all, Apple changes the connector very rarely; this is only the second occurrence in 16 years. Secondly, Apple is actually giving up money to make the switch happen. Not that there’s much money to be made selling Lightning cables, anyway. And all that aside, it’s out of Apple’s hands — USB-C is European Union law.