Aye, if you're using a "standard" ctags executable, we read the "tags" file it creates, as most default ctags implementations don't allow streaming their output to stdout as far as I know. Still, it should not take half of a second to run ctags & read its output file. And if you're using Exuberant CTags
(and specify so in the RText Options dialog, under "Source Browser"), we'll read its output right from stdout.
So assuming you're using some non-Exuberant ctags implementation - if you run it on the command line by itself, outside of RText, does it take that long to execute?