I doubt it was one change on the page - probably 15 individual changes - what does your Page History tell you?
You need to educate the people who are doing the edits ...
If "Notify watchers" is ticked down near the Save button, EVERY time they click Save, an email is sent to all the Watchers
Solution: The editor user needs to untick the option and only reinstate it when they are doing the last edit
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