Fans of the series had speculated this for a while and while many refused to be believe the eventually delay, Atlus has confirmed this as of recent. During their recent Persona 5 PV #03 video, the date of Summer 2016 ended out the video.
So there we go folks, no more 2015 for Persona 5 and a hefty wait until Summer 2016. So get those earlier Summer vacation requests in now. At least we have this pretty video to watch, now if it was only translated.