How to process each record in a large collection (~>500MB)

Question

I have several large collections in a mongo db. some with sizes ~500 MB.

(Collections get bigger over time reaching the 500MB in size and bigger)
    Collection1:
           109091 documents
           total size: 154.3MB 
           avg size of document: 1.4KB
        Collection2:
           102197 documents
           TOTAL SIZE
           15.1MB
           AVG. SIZE
           155B
        Collection3:
           319 documents
           TOTAL SIZE
           115.8KB
           AVG. SIZE
           372B

Collection1 relates to collection2 on the acc field Collection1 relates to Collection3 on the tc field

Only index in each of the collection its the record _id which I don't really use to query the collections.

I am running node js on my local machine: windows 10 RAM: 16 GB

The mongoDB database is in a linux machine which I dont have access to.

I am trying to iterate through one of the collections and process each record while fetching the corresponding record on another collection.

processStream : function(){
    var stream = Collection.find().cursor();
    stream.on('data', function (doc) {
        if (doc.tn !== null && (doc.tc !== null || doc.cTc !== null) && doc.acc !== null){
            //function that findOne per the account field
            module.exports.getAcc(doc.acc, function(res){
                if ( res!== null ){
                    //function that findOne per the tc field
                    module.exports.getProd(doc.tc, function(res2){
                        if (res2 !== null){
                            //write to another mongodb collection
                        }
                    });
                }
            });
        }
    }).on('error', function (err) {
        console.log(err);
    }).on('close', function () {
        console.log('processing finished');
        callback();
    });
}

Then in the routes file I have the following call

app.get('/api/process/', function(req, res){

    console.time('proc');
    functions.processStream(function(){
        console.timeEnd('proc');
        console.log('...operations ended');
    });
    res.json('...processind started');
});

This takes for a long time. The bigger the collection the longer it takes. Is there any other way to loop over a collection in mongoDB and process each of its records any faster? I am sure node/mongodb/mongoose can be used for a lot larger collections (GB?? maybe)..

Taking into consideration the size of my collection just looping through the records in the collections it took 19 minutes.