In the occasion that your animation was intended for R6 rigs, yes. You cannot make use of R6 animations on R15 rigs and vice versa, as the R15 rigs have many more bodyparts (with different names too!), and I am unsure if errors will pop up in the occasion that you try to do it regardless.
Furthermore, it is worth mentioning that Humanoid:LoadAnimation() is deprecated and could be replaced with the humanoid’s (not character, I messed up my bad) Animator instance. You can find more info about this here.