I have a serious problem with this code:

ajaxAuthenticator.Authenticate();

XLWorkbook template = templateBuilder.BuildTemplate();

using (MemoryStream memoryStream = new MemoryStream())
{
    template.SaveAs(memoryStream);
    return memoryStream.ToArray();
}

The problem is in this line

template.SaveAs(memoryStream);

It is taking something like 6 minutes for this line!

I search all around and didnt find any alternatives hope one of you will have.