Same thing here. Any video calls will decrease performance gradually until it freeze the Mac.

Firecop1 The first time it hang at 15 minutes, I just restarted. After that, the update process began again from downloading the Beta again. So I guess you just need to restart

Just to make clear what I did: First try: System Preferences -> Software Update The Beta was downloaded, install began, hang at 15 min remaining message for more than one hour. I gave up waiting and force rebooted. Second try: After reboot, same procedure. System Preferences -> Software Update Curiously, software update downloaded Beta from the beginning again, what makes me think there wasn't a previously downloaded file from the first try to be deleted. This time, the macbook apparently hang at 15 min remaining, but after like 30 min it changed the message to 10 min. After another 30 min, changed to 5 min and so on, until installation process complete. Hope it helps