How do I find the owner of the lost iPhone 15 Pro?

Keep it charged for a day or two and hope whoever lost it calls the phone. If no one calls it, turn it over to the authorities where it was lost. Apple won't give you any information on whose phone it is as Apple never gets involved in lost or stolen devices.

I do want to thank you for wanting to do the right thing. All too often, people come here asking how they can make a phone they found theirs. So it's refreshing to see an honest person who wants to help someone who lost their phone.

SubwaySavvy wrote:

The phone has no service. There’s a SIM card in the phone though (the iPhone isn’t a US model btw). I took it out and put my SIM card in the phone, and it worked, and when I put that SIM card in my phone, it didn’t do anything. I don’t know what now. There’s no way for someone to call the phone if it has no service

Then turn it over to the authorities. Whoever lost the phone likely has had their carrier terminate service on it. There's really nothing you can do to find whoever lost the phone.

Thank you again!

Maybe send the phone back to your relative in Canada, and have them turn it in to a local police station? (Or have your relative tell you the address of a station so you can mail the phone directly there yourself.)

Are you not in Canada?

Ask your carrier how you can call the number on the screen.