Hi Rule1,
I checked out your files, the quality of the model is not so good (inverted vertices, not connecting surfaces, overlapping surfaces).
Has you said it's not more than 1 hour 30min to finish the half helmet (even less) assuming we start from a good model.
As I need to advertise myself I will offer you the model correction which is needed to produce a good .stl file required by 3D printing.
My quote is based on the full project.
Regards.