I only very recently had a bad PC like yours, and even with all the help I got a bare minimum of 30fps in unpopulated areas. If I was you, I'd sort out a cheap PC for the future. When you can afford it of course.
30 Fps is good in my opinion. I can easily play with that i have been playing rust for 333 hours with 10 so.
But the help i wanted is with this command force-feature level 9-3 and all of those. On a thread i read they said they got a 300% fps boost with it but nothing happends when i use it.