Upload file to Amazon S3 from Android slow

I have implemented the file upload to Amazon S3 following the Amazon guide and I have noticed that it is too slow. It takes around 10 sec to upload a simple png file around 20kb.

Initially I thought that the problem was related with threads and I have implemented an AsyncTask to upload the image, but the problem is still there. Following is the code employed to upload the image.

private class UploadFileTask extends AsyncTask<String, Integer, String> {
    String remotePath;
    String remoteFileName;
    File file;
    Context context;
    S3UploadInterface listener;


    public UploadFileTask(Context context,String remotePath,String remoteFileName, File file, S3UploadInterface listener){
        this.context=context;
        this.remotePath=remotePath;
        this.remoteFileName=remoteFileName;
        this.file=file;
        this.listener=listener;
    }

    protected String doInBackground(String... params) {
        credentialsProvider = new CognitoCachingCredentialsProvider(context,
                "MY_PRIVATE_CREDENTIAL",
                Regions.US_EAST_1);
        TransferManager transferManager = new TransferManager(credentialsProvider);
        Upload upload = transferManager.upload(remotePath, remoteFileName, file);
        TransferProgress transferred = upload.getProgress();
        while (!upload.isDone()) {
            try {
                publishProgress((int) transferred.getPercentTransferred());
            } catch (Exception e) {
                listener.uploadFailed(e);
            }
        }
        return "uploaded";
    }

    protected void onProgressUpdate(Integer... progress) {
        if (listener!=null)
            listener.currentUploadProgress(progress[0]);
    }

    protected void onPostExecute(String result) {
        if (listener!=null)
            listener.uploadCompleted();
    }
}

Any idea to solve this problem? Thanks :)