If you are planning to use Direct Entitlement with DPS 2015, you can continue to use your existing Direct Entitlement implementation. The service needs to be implemented with Direct Entitlement API version 2.
Direct Entitlement API version 2
You can build an app by providing the existing integratorId in the App Builder
Request a new integrator ID for your version 2 implementation (contact wwds at adobe.com)
Build the app with the new integratorId
Using 'legacy' DPS 2014 issueList XML
If your current implementation is relying on the issueList XML from DPS 2014 (example), you need to do additional work to integrate with DPS 2015. The account model in DPS 2015 has changed significantly. Through the new Content Services API, information about available collections, corresponding productIds can be obtained. Contact wwds at adobe.com if you need access to Content Services API.