[{_id:1,school:"school A",zipcode:63109,students:[{name:"john",school:102,age:10},{name:"jess",school:102,age:11},{name:"jeff",school:108,age:15}]},{_id:2,school:"school B",zipcode:63110,students:[{name:"ajax",school:100,age:7},{name:"achilles",school:100,age:8},]},{_id:3,school:"school C",zipcode:63109,students:[{name:"ajax",school:100,age:7},{name:"achilles",school:100,age:8},]},{_id:4,school:"school D",zipcode:63109,students:[{name:"barney",school:102,age:7},]}]

db.collection.find({},{students:{$filter:{input:"$students",as:"student",cond:{$or:[{$eq:["$$student.age",8]},{$eq:["$$student.age",15]}]}}}})