Yes, I have tried that too, I mean to open the file in the editor, then the peak memory usage in the task manager was around 5GB.
It's still strange why it peaked to 10+GB at you, because when the file is opened in the editor, then a single line of operation is done in the UCCNC,
that the RichtextBoxcontrol.Text = gcodestring; , so we simply copy the whole g-code text into the Rich textbox control on the editor Window.
In my opinion that does not justifies GBytes of extra memory usage when the file is only about 150MBytes size and is not even formatted in the Richtextbox and so this operation should not eat up much more memory than the file size.