hello bro, friend of mine is using USA bought iPhone 15 pro max and so far no issues bro. I think issue could be specific to your network in particular area. If you are using 5G in Auto mode, do change it to 5G ON.
Monitor for 2 to 3 days how the connectivity stability is.
If same problem repeats, then switch it to LTE connectivity. that will help to prevent network switching frequently between 5G and LTE.
I too experienced in my city, that while network switching between 5G and LTE, internet goes offline and I have to use airplane mode ON and OFF or Mobile data ON and OFF.
So do try and let me know if that helps or not.