You're better just getting the 2019 Pro. The 500 Gig drive on the 2015 model is not some "added bonus".
Out the box, there's no Dolby Atmos support for Netflix and Disney Plus.
Dolby Atmos will work for Amazon Prime, and Vudu.
Via Kodi or Plex, you will enjoy the benefits of Dolby Atmos (Dolby TrueHD/Lossless) and DTS-X (DTSMA/Lossless).
So when you say out of the box no support, can it be added on somehow? I thought for $70 it was going to be a good deal, but now the firestick 4k is sounding better.