Function timing out over large collection

Hello all,
I’m using triggers and functions (Realm apps) on a Datalake to download to an S3 bucket a daily report matching all documents of a collections.
Problem is that for some collections with large number of docs (2.2M) the function is timing out (15s).
Function main code is

        // Match all documents
        $match: {}
        //Convert Date types to String
        $addFields: {
            created:      {$convert: {input: "$created",      to: "long", onNull: ""}},
            modified:     {$convert: {input: "$modified",     to: "long", onNull: ""}},
            activated:    {$convert: {input: "$activated",    to: "long", onNull: ""}}
        //Write results out to S3 bucket in specified file format and size chunks.
        "$out": {
          "s3": {
              "bucket":   s3BucketName,
              "region":   s3BucketRegion,
              "filename": s3pathAndFilename,
              "format": { "name": "json.gz", "maxFileSize": "1TiB"}  //1TiB effectively means a single file will be written

How can I improve this query or increase the timeout limit?
Thanks in advance.