speed of export

hi
I use ExportService for exporting grid to excel
why does exporting work slow? for 4000 rows it takes 20 sec, it is not fine, Is there a way for have high speed in export to excel?
Thanks.

C#
private void ShowPrintPreview(GridControl grid)  
     {  

         SaveFileDialog xlsDialog = new SaveFileDialog { Filter = "XLSX Files | *.xlsx", DefaultExt = "XLSX" };  

         bool? result = xlsDialog.ShowDialog();  
         if (result == true)  
         {  
             System.IO.Stream fileStream = xlsDialog.OpenFile();  
             link = new PrintableControlLink(grid.View as IPrintableControl);  
             link.PrintingSystem.ExportOptions.NativeFormat.Compressed = true;  
             link.ExportCompleted += link_ExportDownloadCompleted;  
             link.ExportStarted += link_ExportStarted;  
             link.PrintStarted += link_PrintStarted;  

             link.ExportServiceUri = "../ExportService1.svc";  
             link.CreateDocument(true);  
             link.CreateDocumentFinished += (s, args) =>  
             {  
                 link.ExportToXlsx(fileStream, new XlsxExportOptions()  
                 {  
                     ExportMode = XlsxExportMode.SingleFile,  
                     TextExportMode = TextExportMode.Value  
                 }, true);  
             };  

         }  
     }  
     void link_PrintStarted(object sender, EventArgs e)  
     {  

     }  

     void link_ExportStarted(object sender, EventArgs e)  
     {  

     }  

     void link_ExportDownloadCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)  
     {  
         if (e.Cancelled)  
         {  
             MessageBox.Show(e.Cancelled.ToString());  
         }  
         if (e.Error != null)  
         {  
             MessageBox.Show(e.Error.Message);  
             MessageBox.Show(e.Error.StackTrace);  
         }  
         else  
             MessageBox.Show("Export succeed!");  

         if (link != null)  
             link.Dispose();  
     }