Your newcomer seems to have been worn by an Unteroffizier mit Portepee (Vizefeldwebel or Feldwebel) or maybe Fähnrich. Are the cockades "clipped" between side posts and shell? Interesting to see this screwable pattern of spike on a M15 Eigentum helmet. More common is the "turn and push out" system like on the M15 EM helmets.
By the way, does your M15 JR92 show some regimental markings?