Using AVAssetExportSession it takes more time to export the large file (around 800 MB)

Hi I am trying to export a video file with size near about 800 MB using AVAssetExportSession which is taking nearly 2-3 mins for completing the process. I have tried by setting the export session preset as AVAssetExportPresetPassthrough, AVAssetExportPresetHighestQuality and others too for try out but didn't work for me as required. Is there any way out over this?

For more details I have given my code following :

let defaultRep = PHImageManager.default()
let str = "\(UIDevice.current.identifierForVendor!.uuidString).mov"
url =  url.appendingPathComponent(str)
defaultRep.requestExportSession(forVideo: self.phasset, options: PHVideoRequestOptions?.none, exportPreset: AVAssetExportPresetPassthrough, resultHandler: { (exportSession, info) -> Void in
        guard let exportSession = exportSession
          else {
            if let error = info?[PHImageErrorKey] as? NSError {
            } else {
            }
            return
        }
        exportSession.outputFileType = AVFileTypeQuickTimeMovie
        exportSession.shouldOptimizeForNetworkUse = true
        let str = "\(UIDevice.current.identifierForVendor!.uuidString).mov"
        url =  url.appendingPathComponent(str)
        self.removeFile(url)
        exportSession.outputURL = url as URL



        exportSession.exportAsynchronously(completionHandler: { () -> Void in
          switch exportSession.status{
          case .completed :
            print("Complete")
            print(exportSession.outputURL)
            print(self.phasset.pixelWidth)
            print(self.phasset.pixelHeight)
            self.mediaType = SBMediaType.SBMediaTypeVideo
            self.videoUrl = exportSession.outputURL
            withCompletionhandler(self)
            break
          case .cancelled:
            print("cancelled")
            if let error = exportSession.error {
              print(error)
            }
            break
          case .exporting:
            print("Exporting")
            if let error = exportSession.error {
              print(error)
            }
            break
          case .failed:
            print("Exporting")
            if let error = exportSession.error {
              print(error)
            }
            break
          case .waiting:
            print("Waiting")
            if let error = exportSession.error {
              print(error)
            }
            break
          default :
            break
          }
        })
      })