There's no reason why you cannot set up 1 core and 15 MDs, and just replay the same video file to each of the MDs. You would want to watch your network bandwidth if the video files are high bit rate, but a gig network could easily handle 15 x SD video streams at the same time. Probably even HD.
Install a core on compatible hardware using the correct networking setup and 2 NICs
Boot each compatible MD hardware on the "internal" network, one by one, and allow each to set itself up
Copy over the video file you want to playback to a location somewhere on the internal network
Tell each MD to start playing back that video file
You are done.