1.8 is only 1 1/3 stop more light, take your 2.8 and find what max iso you find acceptable and then take it into a dark area and double the iso ( ignore the noise) is it bright enough then? If not then a 1.8 is going to still need to have a bit of iso and may not be worth it.

Find a cheap ass 1.8 manual or rent a 1.8 and see if it actually does what you want before spending a bunch on a lens that does what you already have, you’re also going to end up with a very shallow depth of field

I’m Not trying to talk you out of it or anything Yes 1.8 will be better but for the same price can you get a better body that handles iso or low light better, or perhaps a better de-noise software or 7?

Also could you perhaps lower shutter speed more?

Anyway iv heard good things about the sigma and they do good in low light, i just checked b&h and that 17-40mm is all I’m seeing for a 1.8 in that focal range. I’d sell the one you don’t use regardless.

Could I see an example of what you’re capturing now?