We are planning to upgrade from 2.15 to 3.29 which is a major version(s) jump and we don't want our users to feel overwhelmed at the amount of changes they will have to get acquainted with. Not all users are ready for the switch immediately.
It will be nice to have the ability to switch between the old and new interfaces so that they can have a smooth and easier learning and transition curve.
Is the old interface still available to switch to post upgrade?