Omeka 2 Importer for a large collection?

I am currently working on an update to our digital library to move to omeka-S and one of the issue I encounter is with getting our files from the omeka-classic to omeka-S. I know the omeka2 importer module and I have started using it, but the way it works, by getting media files information through the API, downloading them and re-running the thumbnailer operation is very time consuming. It has been running for 30 minutes on my computer for 2000 medias downloaded/converted. For my 300k+ media that would mean more than 3 days of computing, it’s not infeasible but I was wondering if anybody had been working on a way to directly convert the files folder from an omeka2 install to be used in an omeka-s without the need to re-generate all the derivative files?