Have you installed the latest update to 2015 from CC? In some cases you need to quite out of CC and start it up again to make it see updates. Supposedly that takes care of a bug that caused the 100% cpu on export problem but I never experienced that myself.
Yes, I use the latest version of the SS. With all the latest updates. Updating via the Creative Cloud. with the export problems as there are none. disturbed only 100% cpu