Any type of assignment submission is very very slow. regardless is a file or text only assignment.
I have Ubuntu 16.04 in a 2G Ram VPS, and there is no traffic on site.
The strange thing there is that Moodle's timing is saying that it too 0.528 seconds to render the page (that's probably CPU time) but Chrome it saying it too 121 seconds.
So, where is the time going? Do you have anti-virus set up on the server? If so, which one?
No. I don't have any anti virus.