As Saul mentioned Arma is extremely in-optimised all Bohemia interactive games are, it's a issue they've had with their engines for a while. However the server does take up a substantial amount of Potential that you could receive. I strongly advise you look at your launcher's advanced preferences and change some of the settings there for example allow more RAM to be taken up by Arma. Another issue is that your CPU needs to be extremely powerful, as Arma is a CPU intensive game. If you have a good graphics card but a bad CPU the game isn't going to run as well for you.
Kind regards,
Wolfy.