I noticed that my stick was very twitchy when it came to aerial refueling attempts as well, now that I'm alot more used to the F-14 and how she handles I've also reset my curves back to zero.
Can confirm on my end that -15 works well for me, I don't snap the wings by accident now, I have to really yank the stick to actually snap my wings now.
I think adding in-cockpit rattling sounds would add another layer of immersion to the Mig-21, unless the real Mig-21 never had any rattling sounds, then never mind.