Peanuts? not at all.
The LOD sync already takes care of reducing the bone count automatically, and also drop some of the more “heavy” stuff, such as correctives ( completely useless for game characters, even in cutscenes ), hair strands ( also useless for game characters ) skin influence, facial hair, and so on, so unless you use LOD0, you already have performance gain.
@Leomerya12 here there is a comprehensive list of what each LOD does.
So long story short, manually set LOD3/4/5 if you want to have In Editor performances, then if you need switch to LOD0/1 while rendering.
If the performances are still bad, go back to the good old Mannequin setup, and in case have a facial rig with blend shapes such as the one required for ARKit.