IFC stands for Industry Foundation Classes. The classes referred to in IFC have nothing to do with classes and Vectorworks.
I have been following a discussion about importing Revit files into Vectorworks. The user has been complaining that the imported file is 17Mb, and when it is imported in to Vectorworks, the file ends up over 250Mb. This tends to make the files unworkable.
Another use posted a helpful tip, and that was to run the file through the Solibri Optimizer before importing into Vectorworks. This will dramatically reduce the file sizes. You have to register and log in order to use the Optimizer. When you log in, you should have step-by-step instructions.