Arma itself is a very processor base game: your only running on 3.5 Ghz which isn't bad but not the best... If any upgrade consider a processor
also, the problem could be coming from the server itself (no offense lol) but I would recommend trying other severs and seeing if the problem persists if so:
- Try allocating more ram to Windows programs as well as allocating more memory to arma itself
-Or look into new processors (I run on 4.0 Ghz and I still get between 55-65 fps on untra, given my graphics card is a GTX 970)
all of of these options should be explored after running at least two security scans with two different antiviral/anti spyware programs, of course