I am planning to upgrade my phone as well probably to a 15 Pro
As Kurtosis12 has already pointed out, we see a number of problems with users who are purchasing what they think are "new" iPhone 15 Pros.
Even if you can really find a genuine new iPhone 15 Pro, it has been sitting in a warehouse somewhere for 2+ years. This would not be good at all for the battery.
Check to make sure that you are buying from an authorized Apple dealer. You can see a list of authorized dealers in your area using this link:
https://locate.apple.com/
Watch out for other dealers who claim to be "Apple Specialists". They're not..... and more than likely you will wind up with a used or refurbished iPhone with no warranty if you buy from them.
Don't even consider buying an iPhone 15 Pro from an online site. Apple does not have any new iPhone 15 Pros for sale, by the way
Good luck