How to do backup or take copy of collection in MongoDB Shell Script?

I'm trying to do copy a collection to new collection as follows:

db.getCollection('my-orders')
    .forEach(function (myOrders) {
        db.getCollection('my-orders-backup').insertMany([
            myOrders
        ]);
    });

It's working fine for fewer record. But it's taking too much time for more than 20k documents.

Do we have any other way to do backup of a collection?