Church bells coming from Macbook Air

Then you must have some sort of third-party clock app installed that is chiming at the times you've mentioned. Nothing in macOS resembles what you're describing, except for the verbal announcements that you've verified are not causing this.

You should be able to find the app that's running by using Activity Monitor built in to macOS.

Activity Monitor User Guide for Mac - Apple Support

If you look through the list of active apps/processes, look for something related to "clock" or "chime" (maybe). You can then close off the app/process to see which is causing the chime (you'd have to wait the 15 minutes when the chime should be going off). See the guide above to see how to close an active app/process.

You may already have experience with Activity Monitor but I have no way of knowing that, thus the linked instructions.

It may also be a login item that is starting when the Mac starts up. To find out how to disable login items, see:

https://support.apple.com/guide/mac-help/open-items-automatically-when-you-log-in-mh15189/13.0/mac/13.0

System Settings > Control Center > (scroll down to) Clock > Clock Options. Uncheck "Announce the time".

This may not work however since this setting seems to mute the *verbal* time announcements...I don't know about any kind of *chime* you are mentioning.

Maybe you have a different clock app installed that is doing this?

You're welcome...happy to hear that you got it sorted.