I actually think Sony will have more announcements though. They'll probably have one big new game for Fall, and the only thing they have announced for 2016 is Uncharted 4, from a delay, and SFV so they have a lot they can announce. But then you have to take into account they do more conferences than MS as well so I don't know.
Sony has definetly more first party stuff in the works, but how that is going to translate in terms of E3 announcements is pretty much unknown also considering that they usually have a big presence at Gamescom and TGS (and now they also have PSX in December) as well whereas Microsoft still treats E3 as their main and most important event of the year to announce new games.
So it's pretty safe to assume that Sony won't bring all their guns at E3.
Uncharted 4 will be there, Uncharted Collection and Ratchet&Clank will be announced for this year boosting the currently empty first party holiday lineup, Guerrilla introducing Horizon might be the biggest first party news, Quantic Dream should announce their PS4 project (and hopefully for them and their relationship with the gaming press it will be less cinematic than Beyond and The Order
), Level 5 will announce their new project with Sony Japan, Polyphony might have an announcement trailer for Gran Turismo 7.
Then prepare for Sony to promote Batman and MGSV, Star Wars Battlefront will get the Destiny treatment.
Expect more indie games to be announced, others to get a release date (Rime, The Witness, Everyone's Gone to The Rapture) and a few japanese exclusives like Dragon Quest Heroes and Persona 5 to be dated in the west for Q4.
This might be pretty much the Sony E3 2015 conference.
Obviously that would leave a lot of stuff out (Media Molecule new IP, Bend's horror game, Gravity Rush 2, Minna no Sports Resort, The Last Guardian lol, God of War 4 and so on, not to mention the projects that we don't know anything about yet) but those announcements might be reserved for other events.