Seems most CPU time taken by MorphTargetManager._syncActiveTargets, which updates the influence of each morph target. It seems there is a lot of meshes animated morph targets, or a mesh with a lot of animated morph targets.
To optimize for fps, consider reducing the count of morph target per mesh, removing static morph targets, and replacing morph targets with bones if possible.
Oh, wait, seems for mesh with multiple animated morph targets, _syncActiveTargets would be called multiple time for the same mesh, this could be something needed to be fixed.