That 15% protein is way low for most of our birds, and mixing the oyster shell adds too much calcium to an already high calcium layer diet. Change to a 20% protein diet, and have the oyster shell in a separate container. I'd add a grit container too.
Here we don't use the nipple waterers...
Yes, what are they eating? How many feeders and waterers in separate areas? And how many birds? Also, that chicken wire isn't a predator deterrent at all!
If management/ food changes aren't helpful, move the offending hens on elsewhere.
Mary