How do I check to see if my iPhone 15 Pro Max is unlocked?

This is a user to user only forum. Posting your serial number to other users is not wise and I've asked the forum hosts to edit it out for your protection.

We don't know if your new phone is unlocked. Why don't you know whether you purchased an unlocked iPhone? Who did you buy it from to begin with?

You should be able to tell yourself by going to Settings > General > About > Carrier Lock - It says No SIM restrictions, the phone is NOT carrier locked. If it does show SIM restrictions, the phone IS carrier locked.

How can you not know this? Where did you buy it? Ask them.