Yes, you can install both. You should run multiple versions of InDesign.
Use InDesign CS6 or CC2014 for the earlier DPS workflow (with Folio
Builder), and use any version of InDesign for DPS 2015.When you go to
update InDesign, choose Advanced Options and then turn off the setting
to remove the previous version. And if you accidentally uninstall the
previous versions, you can reinstall them. Let us know if that happens
and we can guide you.