Premiere supports CinemaDNG from the BlackMagic Cinema Camera 2.5k, which is what you cite in the thread's title. But in your post, you specify RAW. I've rewritten the title to correctly reflect the scope of your question.
If you're using the DeckLink to send video out to an external monitor, please be aware that Transmit can impact performance. Try disabling Transmit and see if the video plays smoothly within Premiere.
With ultra-HiDef RAW footage, the main bottleneck will most likely be file-I/O -- reading from disk, bandwidth from the storage drive to the processors... Is the content on an internal or external drive? If external, what interface? What's the drive's speed?