There are various reasons for the game performing not at full capacity.
1) Outdated video drivers
You may also visit the site of the manufacturer of your graphics-card and get the latest beta drivers for your card,
as the stock drivers usually update to 'safe' but not to 'optimized' versions for maximum performance and support of functions.
(Also most sold systems are shipped with a default and stable software set, that has been set up a while ago and contains a lot of "older" drivers that do not support als recent functions)
2) Multiple GPUs and using the "powersaving one" to run the game (a pretty common reason for all notebooks, or multi-GPU systems):
If you have another graphics-card in your computer, tell your computer to execute java via GPU only. (In the case of NVidia cards you can do this in the "NVidia Control center")
Adding "javaw.exe" to program list in control center and setting it to 'GPU only' usually fixes startup crashs and lower than average FPS,
3) Java running in 32bit mode on a 64bit OS
Mostly affects windows computers, that use a 32 bit browser and run the automatic installation or update from java.com
Those get falsely detected as "32bit" OS and only the 32bit version of java is updated or installed at all.
to fix that, you should remove all java-versions from your software management on your operating system,
and after restarting your computer use the manual options to install java on your OS by following this url:
Now select "Windows 64bit Offline" to get the most recent version supporting both modes.
If it all does not seem to help, please create a reference installation by using this article,
and send in the whole /logs/ directory after playing a few minutes and encountering the performance problems.
Describe what you were doing while you encountered the FPS-drops or lag, and we will try to find the cause.