I import a biped skeletal mesh into 4.15. It imports fine.
I am using the same character and skeleton to do animations. I bake down the animation and import it selecting the skeletal mesh I already imported so it understands which skeletal mesh to use. When I go into persona and view the skeletal mesh it is fine standing in a T-pose.
However, when I click on one of the animations and show bones in the animation view port of persona the animation is not attached to the T-posed skeletal mesh but shows up on top of the skeletal mesh playing the animation I selected on what looks like a duplicate skeleton. The character is bound and weighted properly.
I believe I have discovered the problem. It comes down to planned obsolescence. I was importing my skeletal mesh as a 2011 fbx file. I imported this file again with a 2014 fbx and the skeletal mesh is behaving as advertised.