Hello Wyldwood!
I am sorry to hear you are experiencing this issue. As you suspected, your computer hardware is likely not the issue here, as it is indeed plenty capable like you've mentioned. The difference between the games you've mentioned not having issues with, and with Elvenar, is that Elvenar is flash based. Sadly, running a flash based application, especially one as resource hungry as this, for an extended time, never really pans out well. The data that is cached through flash applications can become very large, and really bottleneck your system.
With all that being said, unfortunately the best solution here is to not keep the game running for extended times without closing out the session in shoter intervals and reloading the game. It also very much helps and is very much recommend that you clear your browser data (cache, temp files, etc) routinely. Personally, I like to do this about once a week, or sometimes more often if I feel things becoming sluggish.
Also, the web browser you are hsing can have a lot of effect on the performance of the game. Having many browser add ons can also affect this. May I know what browser you are running? Maybe I can make a couple suggestions for you that can help you find a better personal experience for your playing style. Many people have found different browsers more suitable for their personal experience and style.
If you need any help or direction on how to clean out your browser's cache, temp files, or other browsing data, please let me know and I would be more than bappy to guide you.