Examining Effect of MongoDB index using explain

sample_index.log

without a compound index
> db.accounts.find({state: "active"}).limit(15).sort({email: 1}).explain();
{
  "cursor" : "BasicCursor",
  "nscanned" : 11002,
  "nscannedObjects" : 11002,
  "n" : 15,
  "scanAndOrder" : true,
  "millis" : 44,
  "nYields" : 0,
  "nChunkSkips" : 0,
  "isMultiKey" : false,
  "indexOnly" : false,
  "indexBounds" : {
    
  }
}

with compound index:
************ Account INDEXES ************
    state_1_email_1x
    state_1_last_name_1x
    state_1_last_name_-1x
    email_1_name_1x
    doctor_num_1x
    login_1x
    _id_x
    msid_1x
    last_name_1x

> db.accounts.find({state: "active"}).limit(15).sort({email: 1}).explain();
{
  "cursor" : "BtreeCursor state_1_email_1",
  "nscanned" : 15,
  "nscannedObjects" : 15,
  "n" : 15,
  "millis" : 2,
  "nYields" : 0,
  "nChunkSkips" : 0,
  "isMultiKey" : false,
  "indexOnly" : false,
  "indexBounds" : {
    "state" : [
      [
        "active",
        "active"
      ]
    ],
    "email" : [
      [
        {
          "$minElement" : 1
        },
        {
          "$maxElement" : 1
        }
      ]
    ]
  }
}