How bad really is it to have some background noise with open back headphones for gaming?

I’ve been looking into a new headset for gaming, mainly rainbow six siege. I would love to try a pair of open-backs, specifically the PC38X, but have heard obviously they aren’t great in a noisy environment. I’ve never used open back, so I’m wondering how noisy it has to be to actually ruin the experience with the headphones. For example, does having a fan blowing next to the window of the same room distract your ability to hear? Does this make sound imaging worse with the open backs of it isn’t dead silent? I would mostly be playing in a room with nobody else in it with a closed door. Can you really hear everything through the headphones, even normal talking on the other side of the wall? Also, how loud is the sound leak? I’m just extremely unfamiliar with open backs, thanks for the help in advance.