Orc Racial and [On a pale horse]

I was just wondering how do these 2 things go together.

Orc Racial [Hardiness], gives 15% reduction on stuns and [On a pale horse] unholy talent 2/2 gives 20% reduction on stuns (among other benefits).
I was interested - how do these 2 stack? I think adding them up together is too OP, and multiplying them is too underpowered. If we assume Hardiness is the primary stun reduction modifier and everything else calculates based on it primarily, then 20% of 15% is 3%, and that would give a total of 18% stun reduction.

I am greatly interested in what you guys think and know about this topic. It's an amazing talent to have, but having it give only 3% in reduction is a waste, imo.

They add, you get 35% stun reduction from them. With meta socket you reach 45% up to 50%.