Hi SRG7223,
It sounds like you're having an issue charing your new iPhone. While the iPhone 15 does have a different charger port than the iPhone 14, check out the information below from the article here: Charge and connect with the USB-C connector on your iPhone 15 - Apple Support
"Charge your iPhone
You can charge your iPhone with a USB-C cable and power adapter compliant with the USB-C standard, including USB Power Delivery — such as the cable that comes with your iPhone. These cables and power adapters are widely available from Apple and other manufacturers.
Connect the cable to the USB-C connector on your iPhone and to a compatible USB-C power adapter. Then plug the power adapter into a wall outlet.
If you have a 20W USB-C power adapter or higher-wattage USB-C power adapter — like the one that came with your Mac laptop — you can use it with your iPhone for faster charging. You can also charge your iPhone by connecting it to the USB-C port on your computer."
If you continue to see an alert, test the steps outlined here: If your iPhone or iPod touch won't charge
Reach out to Apple Support directly if you continue to have the issue to report it to them and have them further assist. Get Support
Cheers.