Macbook slows to a crawl while rendering in FCPX

Normally there is no need to render unless you have a playback problem. Most users switch off background rendering. The speed of rendering, if you have to do it, is entirely dependent on what it is that has to be rendereded, and also significantly on the graphics capabilities of your system. The 16 GB of RAM won’t make much difference to your rendering speed unless you’re working with large format still images. So, why are you rendering, and what is it you’re trying to render?

Do you have to render? What are you rendering?

It’s down to the graphics capabilities and what you have to render/export, effects, titling, specifics of that can make a huge difference. And of course the length of the project and drive space available. Lots of factors. System drive is too full it’s going to take much longer. Effects like Neat or 3D titles with lighting, reflections, textures, a ton of time and all the resources your machine has just to get through it. Reducing the resources by doing other things on the machine will of course slow the process down further, and none of the applications will function well. If you need to use the web and go to video pages or graphics intensive pages both experiences will suffer significantly depending on card speed and VRAM.