Why do you need to run Open Broadcaster *and* Audacity at the same time? OBS is capable of recording the sound from SuperLemmini and your voice at the same time; you just may have to tweak the settings a bit (getting it to simply record both is easy; tweaking the volume settings can be annoying). The other advantages here is that it can record directly to FLV (which I've found is the optimal format for uploading to Youtube), and you don't have to worry about synchronising the two accurately.
Running more things at once is always going to lead to slowdown; and SuperLemmini is likely already very CPU-intensive due to being a Java app. Therefore, getting Audacity out of the picture should improve it at least a bit. However, if you can't do this, try to run as little else as possible in the background - except for absolutely essential things, close all other programs, especially ones that tend to be quite resource-intensive.
If you've got rid of everything else, but can't get rid of Audacity, try anyway (just as a test run) to record without Audacity running. If it improves things, one very hacky workaround you could consider if you have the equipment for it is to record your voice on a different device (another computer, or perhaps a smartphone) rather than the same one you're recording video on.
