I've have a problem with VPN since macos 15 upgrade, I have M$ Defender too and once I've build our project using xcode, once it finished, it always disconnect VPN, it restarts whole network system and everything was gone, I was unable to deploy to a real device, and I was unable to keep alive VPN for simulators. However after whole day investigation I've found a workaround, just not to use WiFi instead of it I found in the drawer the old a USB Ethernet and a USB A->C reduction ... and now everything work just fine!! So seems to be broken only wifi subsystem, so from my point of view, it is definitely an apple bug.