The file size was abnormally huge so I decided to delete a few 3d objects. Then I deleted all 3d objects and animations just to check if they were the culprit of the issue. But by deleting them the file size only went down to 500MB(from 820MB). Can you please tell me what can be a possible cause for those remaining 500MB?
One possible reason for the file size is User Fields. In your file, even if 3D objects have been deleted, if Resources are not deleted, there may still be hundreds of user field values for each of thousands of Resources.
On very large projects, consider limiting the number of user fields to only those necessary. If you are using Synchro's Revit plugin, you may limit the User Fields exported to SPX by listing only those needed in the Plugin Export settings
Alternatively, you may delete 3D and Resource User Fields and their values after import, by selecting them in the Navigator>User Fields list, and right-clicking to choose "Remove"