Hi Bryan,
Thats a very neat M15 Prussian haube, congrats!
Its well marked. There is BA (Bekleidungs Amt/clothing depot), and ist amrked BA IV, which is a correct Prussian Corp.
Then the oval mark is the maker's mark, cant really read it, perhaps you could post the pics again when you have it.
And there is another numerals mark which I cant also read, perhaps it the year mark?
What surprises me the most is the liner! Thats one very very neat liner, not many haubes have that kind of liner. even the drawstring is also preserved.
The helmet body is still very solid, the eagle wappen is also very well preserved.Both the front and rear visors are also well preserved, they are nt bended, very nice.
As for the chinstrap, I believe its original, the chinstrap buckles are still intact, they are found on each end, near the hook, all we have to do is to re-adjust the lenght of the chinstrap, and placing both buckels in front.
You have a very nice marked Prussian M15 haue there, congrats again. Really Love it!
Hope this helps and cheers,
Mush