I tested it on a dummy and she does about 20% more with Exsanguination.
There's a pretty simple explanation for this: armor penetration only affects kinetic and energy damage (weapon damage is always either K or E). 2 of Nadia's biggest hitters (Run Through and Force Tremor) deal internal damage and, as such, don't benefit from this. In addition, the size of the DoT provided by Exsanguination is friggin' *massive*, not to mention that it's internal so it's not mitigated by armor. I also believe that it is capable of stacking multiple times as each of her attacks is capable of procing it separate (so that each attack's DoT is actually considered a separate ability), but I'm not entirely sure about that one.
15% arpen amounts to all of an ~8% increase in K/E damage dealt. If Nadia deals 1000 dps, Exsanguination would need to tick for only 80 damage *total* to be of equal value as Perforation, ignoring the fact that 2 of her biggest hitters don't benefit from it. Since its individual ticks are bigger than that, you're really just better off with Exsanguination. I'm pretty sure the same is true for all mdps companions.