No Madden 16 Demo or Beta
We do not expect a Madden 16 demo at all. Although previous Madden releases included a demo, this is not something that EA delivered with Madden 25 or Madden 15.
Update: EA confirmed no Madden 16 demo.
It is also unlikely that EA plans any kind of Madden 16 beta to test multiplayer gaming or settings. Although there are typically hiccups with the first week or two of online gaming following the Madden 16 release, this is not something that we expect to see a beta test.
Based on the previous actions and the lack of any communication about a Madden 16 demo or Madden 16 beta, we don't expect either to arrive in 2015.