Well, currently I have a much lower PC than yours and I can play without problems, sometimes I have a little low FPS in Castle Siege but nothing more.
According to my experience and what I know this game was created in a very old version Unreal Engine graphics, for this reason this game has many performance problems in newer components.
Example,
On this PC I can play 23 stable FPS
i3 2120
8GB Ram 1333 ddr3
GTX 750 1GB DDR5
And then I have another high-end PC with GTX 1080 and it is impossible to play, another important fact is that some people add many new textures to the client and that only slows down the load times.
I use BLADE Anti-Lag with the original effects of the game, I manage to have the most stable game when I install the anti-lag and then paste the original backup from the Effect folder.
Also other programs to reduce latency like, WTFast, PingZapper, BattlePing, ExitLag.
remember to read the rules of this.
before running this command open task manager
Another good solution to free up system memory is to open the CMD and run the following code.
taskkill /f /im explorer.exe
and you will only see the game on the screen, to see the taskbar again just open the task manager and run
explorer.exe
I hope I can solve your doubts and help you, I hope you can understand my humble english...