Try and increase the server time-out limit

Step 1. Click on Files 

Step 2.  Click on Account settings > Account settings

Step 3. Double Click on the account


Step 4. Click on More Settings and then Advance tab


Step 5. To increase the Server Timeout, Under Server Timeout drag the Slider the way to your Right


Step 6. Click Ok

If you are still sitting with an issue after, Compress the File, File types that are reduced the most after zipping are text-oriented file types such as .doc, .txt, and .xls