I checked your file in MS Excel manually. I spotted there are billions of pages (mostly pages are blank (after page33 or so)) when taking the print preview of the sheet for the range A1:XEM1048483. So, you can imagine how much time, CPU and memory would be required to render this huge list of pages by SheetRender APIs. I guess the time consumption is ok for rendering billions of pages. Why you are rendering the blank pages? You may easily cope with it by setting the attribute for ImageOrPrintOptions. See the sample code for your reference:
var imgOptions = new ImageOrPrintOptions
PrintingPage = PrintingPageType.IgnoreBlank,
ImageFormat = ImageFormat.Png
Alternatively, you may try to use the following lines of code to remove blank rows and blank columns:
//Delete the Blank Rows from the worksheet
//Delete the Blank Columns from the worksheet
Hope, this helps a bit.