LMMS Performance Tips?

Having trouble with LMMS? Ask about it here.
Recently I've become acquainted with the CamelCrusher VST. I usually don't use VSTs (except for mastering), but I fell in love with it immediately and I use it on most of my percussion. The issue is, it's a bit of a CPU hog and LMMS freaks out whenever I use more than three or four of them.

When the CPU gets out of hand, the sound starts stuttering, and LMMS skips many notes.

I have already read Brandystarbrite's guide for LMMS performance, and I was actually already doing most of those things. I have a really old computer made with spare parts in my grandparent's basement, so it usually runs quite slow.

This might be related, what does the Buffer Size in the General Settings do? Where should I have it set, ideally?

Is there anything else I can change in the settings to allow LMMS to run faster?

I've even removed all other VSTs I had on there with the intention of adding them back at the end (since they're for mastering), but that didn't really help much.

I'm running Debian 9, if that matters.
The buffer is how long LMMS is allowed to wait before playing what is at the playhead is the simple answer. A longer buffer means higher latency, but also helps slower CPUs keep up without overruns (audio glitches from the CPU skipping regions).

If your buffer is maxed out and you're dead sure that nothing else is running on your computer, the sad answer is that you'll need a better computer or find other less resource heavy plugins. A last ditch effort could be to render your percussion or whatever uses the VST and loading it back in as a sample to save CPU.