I had previously increased the dbcache value to 160000 MB (with 16 GB of ram).
That's 10 times more than your total RAM, that's not good. I don't expect it to use that much though, but just in case: have you checked how much memory Bitcoin Core is using? If it's filling up your swap that could cause a dramatic drop in performance.
I usually set dbcache to 4096 MB when I'm downloading the full blockchain, and reduce it to 1024 for normal continuous usage (when I have a complete blockchain already, and only need to download a few new blocks per hour).
Thank you for your answer. I have just tried by setting the value dbcache=4096 in the configuration file.
Unfortunately it doesn't change much.
It caps according to the task manager) 30% CPU usage and 400 MB used in RAM. And 0.1 MB /s for disk usage.