Try to delete preferences. But be aware that CS6 was never intended to work with El Capitan. It happened to me also in the beginning that CS6 was slow on 10.11, but became better. But normally I work with CC2015 which is much faster and is compatible with El Capitan.
Hi Willi, where do I go to delete the preferences?
Ignore my comment, I found how to do it (holding shift, ctrl, option, cmd when starting indesign). Unfortunately it made only a tiny difference, its still definately shorter than it once was. Any other things I could try? I have already switched off flight mode and my font book's font auto-activation, because some one else recommended that.
Maybe it might help to reduce the number of fonts which is installed?
Not to use T1 fonts anymore?
Not to use PostScript like EPS?