What happens if I remove iOS 15.7 from my iPhone 11?

Removing the beta profile will be required if you want to upgrade your phone to the latest version of the released iOS.

Ref: How to uninstall iOS or iPadOS beta software - Apple Support

When you elected to install a beta version of iOS, you were informed that doing so is at your own risk. If you did not backup your data BEFORE you installed the beta, then you will have no way to recover it should removing the profile, itself, prove unsuccessful and require that you need to restore the phone.

FWIW, it has been my experience with iPhone betas (so far) that just removing the profile did not remove any data on the phone, other than the profile itself.

Not exactly sure by what you mean by "remove" iOS 15.7 from your iPhone. Could you please explain what you are trying to do exactly?