I am experiencing this exact issue. I have my account and my two children's accounts set up in a family plan, although they've never played Minecraft on this PC.
I joined the RTX beta through Xbox Insider Hub last night. I did have to wait quite a while in the "pending" state for it to update. Insider Hub then opened my Windows Store and started the download. RTX looks great but I wanted to get back to the Realm I share with my kids.
This is what Xbox Insider looks like now:
[media]It no longer shows me as enrolled in anything and clicking unenroll does nothing.
I've tried all the "usual" methods mentioned in this post as well as https://bugs.mojang.com/browse/MCPE-33270
I don't have this behavior at all. When I uninstall Minecraft the uninstall cleans out any Microsoft.MinecraftUWP_* file from WindowsApps. I'm already unenrolled through Xbox Insider Hub. Upon reinstalling, 1.15 shows up again like some sort of dirty wizard magic.
I tried Larry's suggestion to just delete the 1.15 by brute force but could only do that while the game was installed. The Windows Store wouldn't give me the option to reinstall until I used the uninstall process. Not really sure what I expected but I'll try anything short of wiping my harddrive at this point.