Moderator elections are not scheduled events. Instead, they are brought up as the need arises, namely when more moderators are considered "needed." As you can see from the elections list, there was no scheduled election for 2015, because no new moderators were needed.
To be more exact, moderator elections typically happen when the community moderators contact Stack Exchange and ask for an election. Similarly, an election may also be triggered if Stack Exchange notices that the current mods are being overwhelmed by the duties of the site (flag queues, closevote backlogs, etc.). Stack Exchange also contacts a site's mod team at the anniversary mark from the last election to ask the question, but this still does not guarantee an election will take place. (Source).
Unless SE or our local mods really need new moderators now, the next one is likely to happen in June 2017, but this doesn't mean it will happen then.
Moderator elections tend to take 15 days, and are split up into three "phases": Nomination, the Primary, and the Election. Instead of boring you with the details, I'll just gloss through them real fast:
- During the Nomination phase, which lasts 7 days, any user with a minimum sufficient reputation (variable) can nominate themselves to the ballot.
- The top 30 users by reputation move on to the Primary phase, where anyone with at least 150 rep can vote for them. Note that if 10 or less candidates nominated themselves, this phase will be skipped.
- The top 10 users (by votes in the Primary phase) will be moved on to the Election phase. The winners will be chosen using the Meek STV method.
