Alex,
One-piece of advice you will hear over and over again from members of this forum is to evaluate the piece -- not the write-up. In the description the author talks about the reserve battalion of the infantry Regiment. That is not how it worked --
So if you disregard the description and concentrate on the helmet you will discover whether it is good or bad. This allegedly is a helmet with a Landwehr cross from the small principality of Lippe-Detmold. There is a Landwehr cross, a Prussian type Wappen, a very different cockade. It is marked to infantry Regiment 15. It is also marked to VII corps.
Using this information and perhaps other information that you have drawn from the pictures what do you surmise? The starting point Socratic question would be what unit came from Lippe?
I am just trying to make you follow the same logic trail that others follow - sort of a Socratic teaching method - if I'm being obstinate let me know -- it is not my intent.