In reality, each of those 15 people do a very specific, probably undefined, but valuable task.
There's always some random spreadsheet, or paperwork, or approval that only they know even exists. Or they know exactly how to get that one important system back online when it fails every 6 months.
Management sees those 15 people walking around and think they can just fire them and only get the benefit of the 3, but in reality, it just pushes those tasks to the 3 folks and makes them even more overworked.
Not everyone needs to be heads down at their desk for 8 hours a day, 5 days a week to be valuable.