The 15th Virginia Infantry was mustered of men from and around Richmond Va.
I did not locate a Hartwell Barham nor a Captain Mason associated
with this particular regiment. I checked both 15th Infantry and
Cavalry Regiments as well.

Same as you found I located a Hartwell F Barham that enlisted in
July 1861 into the 2nd Tenn Cavalry Battalion (Biffles). He was
listed as being 23 years of age on enlistment. In May 1862 this
unit was merged into the 6th Tenn Cavalry Regiment. In those records
there is a Captain Hartwell Barham in command of Company-I of this unit.
He ended the war and signed the oath and parole in Charlotte NC on
May 3rd 1865.

The 1860 Census for Perry Tennessee has the following:
- Hartwell Barham (b.1839)
- H. Barham (b.1807)
- Nancy Barham (b.1812)
- George Barham (b.1837)
- Henry C Barham (b.1842)

Frederick