New synology DS916+ (successor DS415+ ?) vs DS1515+ for plex server?

Hello, i saw today that the new synology DS916+ is released, i think this is the successor of the DS415+, but correct me if i'm wrong! :p I was thinking about buying a nas for plex server, and backup. I want to get rid of my old mac mini and my stack of hard drives laying around. (I use it to stream to my ATV 4) Which one would you advise the DS916+ vs DS1515+? Or should i wait for a 2016 version of the DS1515+? (the dS1516+ is suppose) I can wait a few months...
( https://www.synology.com/en-global/products/DS916+#spec)