After effects music visualiser project last 3 minutes take forever to export

Hi everyone, I am really stumped. 

Basically I have been making music visualisers on after effects, most have been about 3-5 minutes long however I recently got given a 16 minute long one. Now I am very new to after effects and export times although being kind of long haven't been too bad. 

This 16 minute composition I decided to export a few minutes at a time using the work area and selecting the first 5 minutes, then the next 5 minutes, the next 3 minutes and then the final 3. The trouble I am having is with the final 3minutes. Currently it is saying 66 hours to export and that number just keeps increasing! It seems to be making no progress and I really don't understand why. Does anyone have any ideas? I am not doing anything different to how I exported the rest of the video. 

If you need more information about the project I am happy to give it I'm just not sure what info people will need to help me.