When I find myself in an indoor environment or one that isn’t super well lit with a lower ISO film, I’m always nervous to shoot at slow shutter speeds.

1/15 while standing and 1/4 while leaning on some walls

1/8s without any supporting platform, 1/4s with one

I got this at 1/15, but I wouldn’t say I was “comfortable” with that choice.

Quite often hit 1/15th with the 50mm.

One over focal length

1/8 or 1/15 on my Mamiya 7 or RZ67, 1/30 maybe 1/15 on my 35mm cameras.

This is on 1/30th, but I can go lower if needed, I’d say 1/20th things start to get a little shakier, I’m getting better at it though.

60

That would be determined by the focal length of the attached lens.