Whoops, I did look to see if you had a signature with specs, but I was looking for it in the window where you post a reply, which hides the signatures apparently. 
Hmm, yeah…16GB would seem enough to me. But you could check Windows Task Manager to see if it’s maxing out RAM. If so, a RAM upgrade might do the trick. But it does seem it’s most likely the HDD that’s the bottleneck. But it’s hard to say, as I don’t know exactly how much data you have going on in the project and how Cubase handles this exactly.
I can’t imagine getting an SSD for my audio HDD at this point, prices are still ridiculous! 
Good luck anyways!