linkOsPrinter.downloadTtfFont(..) executed too long

Hello, I'm using android sdk , here is my code:

  1. Connection connection = new BluetoothLeConnection(macAddress, this); 
  2. connection.open(); 
  3. ZebraPrinter printer = ZebraPrinterFactory.getInstance(PrinterLanguage.ZPL, connection); 
  4. ZebraPrinterLinkOs linkOsPrinter = ZebraPrinterFactory.createLinkOsPrinter(printer, PrinterLanguage.ZPL); 
  5. linkOsPrinter.downloadTtfFont("/storage/emulated/0/fonts/DroidItalic.ttf", "Z:Droid"); 

downloadTtfFont(..) -- this method executed more than 2 hours,(file size is 174kB) ? is it normal?  can I do something to reduce execution time?

Thank you in advance!