CS6 has no support under El Capitan. There have been numerous reports of all kinds of issues here.
The best advice is to roll back to a supported operating system. CS6 has reached EOL and will not be updated again.
Sorry to burst your bubble there Bob, but I spoke to Adobe support on the phone last week as we have both InDesign CC 2015 and InDesign CS6 and I was told that if they release updates for ID CC 2015 that are relevant to CS6 they will push it out for CS6 as well. I've seen updates to it every now and then, though very rarely.
Why else would Adobe's bug reporting tool still be up and accepting bug reports for CS6, and why should I NOT be posting things about it in case other users around find fixes that they discover by themselves that will work for me as well and the rest of the community?
Obviously we know CS6 isn't officially supported on El Capitan, but when I asked on the phone, the engineer said that updates will still be released if they become available and are created, it's just that there is no more live support from Adobe for CS6.
I really don't appreciate your negativity on this, and, as you are not Adobe staff, I won't lend much credence to what you say.
Thank you for posting though.
Does restarting CS6 help you any in terms of performance? If so just restart it once a day. We always just did a shutdown at night and that worked for some of our computers. Others were really finicky and would crash several times even after restarting.
The amount of features fixed and added since cs 6 would be worth upgrading. If you can afford it