my new iPhone 15 drops internet connection

Joe ~ Apple's iPhone User Guide says: "If your iPhone isn’t working as expected, you can try restarting it by turning it off, then turning it back on. If turning it off and on doesn’t fix the issue, try forcing it to restart.":

Turn iPhone on or off - Apple Support

Also, see if step 7 (Reset your network settings) here helps:

If your iPhone or iPad won't connect to a Wi-Fi network - Apple Support

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I have been having similar problems since the penultimate IOS update. My previous iPhone 12 never had problems with WiFi connectivity. I use a VPN (tried two suppliers) and have asked them if they can offer any advice. Been told to reset Network settings which helped initially but the problem has since returned. My wife has an iPhone 15 but is with a different network and has exactly the same problems.