Zenimax Online Studios announced some of the first details for the Update 15 and next DLC coming to The Elder Scrolls Online today. I mean, they announced the new details today, not that the update is coming today.

Anyway, the next DLC is called Horns of the Reach and will be released in August. That will be content you have to pay for. Update 15 is free to everyone.
The Horns of the Reach DLC Game Pack includes:Free updates coming in Update 15 include:o NOTE: Battlegrounds PvP is only available to players who own ESO: Morrowind

A few additional details on both the DLC and Update 15 can be found at the Elder Scrolls Online website.