Did you mess up the nest on the floor? When my BO made a nest on the floor of the coop, I took a stick and messed it up. Not so easy to come back to it, ya know?
I put in your other thread that my BO took a week to make it to the nesting boxes. She'll get there.
Besides, with 15 chickens, SOMEBODY is bound to make it to the boxes when they start laying and the rest will copy. I haven't seen any of my chickens do things by themselves. One does...