The Olog-hai is an interesting option. For The Silver Bayonet I always thought those models looked too brutish, but you’re right, they make very good 15mm Ologs!
The key thing for the Ologs is that they can't be wearing too much:
[There] came striding up, roaring like beasts, a great company of hill-trolls out of Gorgoroth. Taller and broader than Men they were, and they were clad only in close-fitting mesh of horny scales, or maybe that was their hideous hide; but they bore round bucklers huge and black and wielded heavy hammers in their knotted hands.
I was wondering about some hammer-wielding Prince August orcs (I think I have three or four different types with hammers), but most of them are a bit overdressed to be trolls!