You might be right. I think Warrior Mutator boosts it to 50. Which doesn’t sound like much. But when combined with Agility bonuses and such, it was the only way to hit over 90% DR. Going from 85% to 90% doesn’t sound like a big jump. But a 30 dmg attack to 85% is 20 to 90% and it adds up, especially against some of the creature capable of 750+ dmg hits added by some other mods.
But this is getting a bit off tangent. In either case it should be 50 at least, or maybe even +3-5% or something other than just 15.