is it possible to connect iPhone 15 to a printer directly with a cable?

No, it's not. You'd need printer drivers installed on your iPhone, which isn't a possible option. Either you need to have an AirPrint capable printer, or one with an app you can print from.

No.

Actually, you can connect the iPhone directly to a printer with a cable and the right adapter.

But......you won't be able to print that way.