Could you specify the timings on your side, what is your configuration and what are your expectations? I was able to import such document in about a 30 seconds, which is not ideal, but acceptable for such large documents. Sharing the actual document could also help - in case the issue is related to a specific feature in the document.
Looking forward to your reply.
Do you need help with upgrading your AJAX, WPF or WinForms project? Check the Telerik API Analyzer
and share your thoughts.