Particularly I liked Ernst Weckerlings story! The short episode at the end of his interview is the only period source I know of that tells something about the handling of removable M15 spikes in practice.
He says the spikes were collected in bags before the battle, so it wasn't the soldiers keeping them. Maybe it generally was not an individual decision when to remove them. As these bags were lost in the fierce fighting, the men carved false spikes from potatoes before marching up for the emperor in a ceremony.