You can continue to make content in the existing system. One way to do what you want without too much effort is to continue creating content in the current system, and then use the content migration tool to migrate that content over to DPS 2015. It'll save you the hassle of having to upload the content twice, yet still give you the flexibility to use the new DPS 2015 system with content you're producing for the current system.
You can even follow this model to try releasing an updated version of your application on another platform (Android or Windows, for example) to try out new experiences there before bringing those experiences over to your primary platform (iOS, I assume).
Neil