I'll make some extensive predictions (with some wishful but realistic thinking thrown in)
Bethesda
- New DLC trailers for The Evil Within and ESO
- Doom gameplay, Beta out that week
- Battlecry trailer
- Teaser for MachineGames new project
- Dishonored 2 and Fallout 4 announced, one will be late 2015 the other late 2016. Which ever is out this year will also appear at the Microsoft press event.
Microsoft
- Lots of time spent on Halo
- Call of Duty
- Quantum Break demo
- There will be no gameplay for phantom dust
- Forza
- Crackdown Trailer
- Gears Teaser
- Scalebound gameplay shown, out 2016
- At least one old rare property will be mentioned in some way
EA
- Lots of Star Wars Battlefront, including single player demo at Microsoft/Sony, Online demo at their conference. Out November/December this year.
- Mass Effect 4 trailer, out 2016
- some sort of racing game
- New Dragon Age DLC, out within a month
- Mirrors edge trailer that doesn't show much, out late 2016
- SPORTS
- Titanfall 2 announced (most likely shown at Sony), out late 2016.
Ubisoft
- AssCreed Victory / The Division / Rainbow 6: Seige will all appear at both Ubisoft and sony/Microsoft press conferences
- Seige will also now be a 2016 game
- Just Dance
- New Rayman game (pls)
- Watch_Dogs 2 announced, out late 2016
- End on something surprising, I'm feeling an rpg this year but it will probably be a TPS with rpg elements
Sony
- Big Uncharted 4 demo, game still said to be out 'holiday 2015'.
- Either The Order or Bloodborne will see a DLC announcement
- Destiny DLC
- Short God of War trailer, gameplay for PSX
- Too much time spent on Morpheus but at least one big game will be announced for it
- New Trailers for MGS5 and FFXV
- Metal Gear Rising 2 PS4/PC exclusive
- New SF5 trailer
- INDIES
- The vita will have one new game announcement, either of a remake or cult game (I feel FF12HD, also on PS4, or Zero Escape 3, co funded by Sony)
- Horizon shown, out within a year
Nintendo
- The Legend of Zelda Demo, Holiday 2015 but will later drop
- Star Fox Wii U, Holiday 2015 and makes it
- Metroid teased
- New Xenoblade trailer
- AMIIBOS
- Pokemon Z/ XY2