you haven't noticed this in other languages because they are built in Notepad++ and they are not using the plugin libraries.
To resume the situation , all languages coming in an external plugin are yet slow, this is a bug from the plugin library, not the plugin itself. It affects GmodLua, LuaWoW, External Lexer KVS, Oberon-2 Lexer, and more.. all the one you see in the Plugin Manager are plugins affected by this issue.
if the library is slow, all plugin languages based on it will be slow.
We can only wait a patch to the library (scintilla) and don ho will include it then in Notepad++ and the language plugin will be faster.
Of course this is not a failure of your computer but the fact that you've noticed it is slow with only 6000 words recognized is abnormal and I'm not sure the scintilla speed patch will be better for you.
I suggest you invest in the i7
