Yep, the import is slow. I know and I haven't done much optimizing in the code. The Route I'm going is

1. No Tool
2. A Tool
3. A fast Tool

And I'm currently working on 2.

— From https://github.com/MaZderMind/osm-history-renderer#readme

A spin on the “Make it work. Make it right. Make it fast” adage but I enjoyed seeing it in the wild. I feel like I'm almost always working on step 2.