Ruby Dragon extends Ghidra with support for several programming languages beyond the base Java and Python 2 (Jython) options. Each language is implemented in its own plugin, and includes both an interactive interpreter similar to that of the Python interpreter (REPL) as well as support for writing scripts in the supported language. The only exception to this is JShell, which only provides a Java interpreter (since Java scripts are, of course, already a core feature of Ghidra).
Ruby Dragon embeds the languges it provides into the Ghidra environment, which of course comes with a performance cost. In some cases this cost can be significant, leading to a slow (and therefore bad) user experience. Here are a few ways that you can reduce the impact of using Ruby Dragon in your workflow.
Each language supported comes with its own set of performance impacts, and these vary per-language. It's likely that you have one or two particular languages you want Ruby Dragon for, instead of all of them. Disabling the languages you have no use for will keep them from causing performance impacts by running, and also reduce clutter in your tool UI.
You can disable the plugin for a given language by going to the File menu and selecting Configure in the CodeBrowser tool, and unchecking the plugin in the plugin list. Ruby Dragon plugins are installed to the Ghidra Core category so that they appear alongside the Python plugin.
Ruby Dragon supports a set of classes being automatically available in each interpreter session, to reduce/remove the need to manually type import statements (or the equivalent) in your REPL. However, this will cause a delay in the startup of the interpreter, often on the order of several seconds. This feature is disabled by default, and can be adjusted on a per-interpreter basis in the tool options menu. If you've turned it on, you can probably save yourself some time by tuning the auto-import list to only pull in classes you need. The auto-import list is in an XML file in the data folder of the extension installation named auto-import.xml.