[{"_id":"oidfi","users":[{"_id":"q","tags":["a","b","c"],"age":20},{"_id":"q","tags":["x","y","z"],"age":30}],"type":"repo"}]

db.collection.aggregate([{"$project":{"users":{"$filter":{"input":"$users","cond":{"$and":[{"$gte":["$$this.age",15]},{$gt:[{$size:{"$setIntersection":["$$this.tags",["a","x"]]}},0]}]}}}}}])