>>31582661/focal length is a bit of a meme, as it has nothing to do with your ability to hold the camera still, and everything to do with the choice of focal length's likelihood of magnifying any movement to the point where it's visible.
If you can get a sharp shot at 1/15, you can do it with a 15mm or a 100mm.
If you're full Michael J Fox, you might need to be at 1/125 to eliminate camera shake.
Usually anything above the sync speed will be quite sharp though, regardless of focal length.
If I'm shooting Tri-X or HP5 in the dark, I'll usually just leave the shutter speed at 1/15 and shoot wide open on a fast 50mm and let the exposure be what it is. This was with no room light whatsoever, just fairy lights on a stage. It's basically as low light a situation as you could even imagine taking photos in, and the photo is sharp. Yes, I could clean this neg up to get rid of the dichroic fog, dust and watermarks, but it's just a shitty gig photo.
