Unfortunately, your statement tells me that I know far more about this than you do. What part of my statement that I have tools to test these things was not clear?
I am an experienced Mac tech with clients who need me to know and understand such matters. 16G is the bare minimum as far as I'm concerned unless a sealed system that never accesses the internet. The apps I use to make my living would cause my system to freeze if I did not have 32G on board—as they did before I upgraded.
My opinions are based on my testing and experience and not nonsense that others found on the internet written by guys in their armchairs.
The OP swaps in and out of an ancient (over 5 year old) spinner. So, while 8G RAM shouldn't be the cause of his slowness, having no idea the health of that drive nor knowledge of the apps being run, I can only take a blind guess and state that it probably isn't the problem—but it can be. Only on my bench could I be certain.