Wizards of the Coast will release Magic: The Gathering – 2015 Core Set in July. The 269-card set will be available in Booster Packs, Intro Packs, Fat Packs and the new Clash Packs
The 269-card set is slightly larger than the 2014 Core Set, which had only 249 cards.  So far the two spoiler cards of note are "Waste Not" and "Wall of Fire," which were both used as examples of the new card design changes debuting with this set (see "First Look at 'MTG: 2015 Core Set'").  The tagline for the set is "Hunt Bigger Game."
Another new addition debuting with this set is the Clash Packs.  Wizards was quick to point out that the Clash Packs are not replacing Event Decks, but rather will alternate with the Event Decks for set releases.  (In M:TG set slang, if there is an Event Deck for the "Huey" release, then there will be a Clash Pack for the “Dewey” release, and back to Event Deck for "Louie.")  Intended as a way to introduce new players to higher level play and customization of a deck, the included instructions show players how to combine cards from each pre-constructed deck to create a new deck equal in power to an Event Deck.  The two-player Clash Pack will come with two ready-to-play 60-card decks, six premium foil cards with alternate art, a deck box, a strategy insert, and a M:TG rules reference card.  MSRP is $29.99.
WotC will support the release with the normal program of events.  Pre-release events will occur on July 12-13.  Launch Weekend will be July 18-20.  The Pro Tour Event will be held in Portland, Oregon on August 1-3.  Game Day will be August 9-10.
Aaron Forsythe led the initial design team for the M15 set, while Billy Moreno headed up the Final Game Design and Development Team.  The 2015 Core Set follows the release of Journey Into Nyx, the third set in the Theros  block (see "'M:TG--Journey into Nyx'" and "Top 10 'M:TG--Journey into Nyx' Cards Before and After the Pre-Release").