Strange Performance Drop With Skeletal Animation

I have a problem regarding skeletal animation. I made a skeletal animation system and I have imported some models with animations that a friend made for me, and so far it’s been working fine except we had a problem with one part of the mesh being transformed the wrong way so she solved the problem by adding one more joint and now it renders correctly. The only problem is that with the new rig I got a 20 fps drop, which is huge considering she just added one joint. What could be the cause of this? Even if the animation has fewer keyframes it’s the same result.