What you need to do to speed up your PC really depends on what part of your PC is "resource bound." In other words, out of all components, what is tailing all others in terms of performance.
It could be your CPU, memory, video card, or disk.
Windows OS has "task manager" and in it, a "performance" tab that will show you what is maxing out.
I suspect 16GB is enough for what you are doing. CPU isn't usually the slowest part. I'd bet it's your disk. Here, going from regular hard disk to solid state disk will give you several fold performance boost. But that's all guessing. Performance monitor will tell you what is lacking.
I don't use Lightroom but I use PhotoShop CC. I have dual Xeon CPU with total of 12 cores and 40GB of memory. Unfortunately, Photoshop does not use all of the CPU resources. Although I have a lot in terms of processing power, I find typically few cores maxes out while others are just idling. Memory usage never goes over about 12Gig or so.
Here, I could go to faster clock rate rather than more cores, but that's a lot of money for upgrade. Until Photoshop programming improves to better use resources, nothing else I do will improve my result. All this became obvious watching the performance monitor.