[{_id:ObjectId("545a0b63b03dbcd1238b4567"),status:1004,comment:"Rem dolor ipsam placeat omnis non. Aspernatur nobis qui nisi similique.",created_at:ISODate("2014-11-05T11:34:59.804Z")},{_id:ObjectId("545a0b66b03dbcd1238b4568"),status:1001,comment:"Sint et eos vero ipsa voluptatem harum. Hic unde voluptatibus et blanditiis quod modi.",created_at:ISODate("2014-11-05T11:35:02.814Z")},{_id:ObjectId("545a0b66b03dbcd1238b4569"),status:1001,comment:"Sint et eos vero ipsa voluptatem harum. Hic unde voluptatibus et blanditiis quod modi.",created_at:ISODate("2014-11-05T11:50:02.814Z")},{_id:ObjectId("545a0b66b03dbcd1238b4570"),status:1001,comment:"Sint et eos vero ipsa voluptatem harum. Hic unde voluptatibus et blanditiis quod modi.",created_at:ISODate("2014-11-05T11:51:02.814Z")}]

db.collection.aggregate([{$setWindowFields:{partitionBy:null,sortBy:{created_at:1},output:{count:{$count:{},window:{range:[-15,15],unit:"minute"}}}}}])