the tag "equipment" does not work in the snapshot 15w34b. You can use this command, you should bring up a "armor stand" in leather armor
/ summon ArmorStand ~ ~ 1 ~{Equipment:[{},

{id:"leather_boots",damage:0}

,

{id:"leather_leggings",damage:0}

,

{id:"leather_chestplate",damage:0}

,

{id:"skull",damage:3}

]}