I'm trying to reproduce your issue and I'm unable to do it here -- even with those constructs, it doesn't get slower, so, I think your real issue is some other issue -- the most likely is that the JVM is not getting enough memory.
So, please try doing the following: turn the build automatically on again (if you disabled it -- as it's not generally recommend) and check:
If you have the latest PyDev installed
Is "OpenGL" in the forced builtins (it should be -- that should be done automatically, so, just double-check).
Read What are the best JVM settings for Eclipse? and use those settings (if it's really a memory issue, the "-Xmx" flag is the one you need to raise).
If nothing solves that and you really feel disabling the automatic build is needed, don't forget to run the build manually whenever you use some function that needs that info -- i.e.: search globals: Ctrl+Shift+T, find references: Ctrl+Shift+G in selected token -- and probably a bunch of others I'm forgetting :)