Hello Kayla12S,
Welcome to the community!
Apologies, but I'm not quite sure I understand your situation. Could you please elaborate on your concern? I assume the phone to which you refer is your old device? When you returned the iPhone 15, had you used it with an eSIM? If you did, you would likely need to obtain a new SIM card or eSIM for your old device as the one it was using would no longer be active.
Hope this helps 😀
Cheers
