How much should I limit my FPS for a smooth recording

Hello everyone, I am super new to OBS or anything to record games. However I wanted to record a new let's play and realized that it was so laggy that it become unwatchable. I know that I can limit the frames and I will try that however, the game I am playing is rather old and I have limited it to 30 fps. Is it enough to still have a smooth recording or do I have to change my game to 60 fps. If not, is there any change I have to do in OBS itself?

My computer isn't a bad one but a bit older. I think I got it in 2017 but has a graphic card and can keep up with every game (I have played GTA5, laracroft, sims,...). I heard some people said that maybe the computer just won't work with the system and if that is the case, is there another software I could use or is it just a lost cause?