Cannot Import Large RSS Feed

I am trying to import a file in RSS format that has over 8,000 items. I’ve tried saving it as an XML file and uploading it but when I click check data nothing is shows. The file is just over 14 MB in size.

I also tried uploading the file to a website and accessing the URL. In that case I get as far as preview before the preview shows nothing for items, but will show for images.