[oftenwrong]

For the "move to subdir" step, I recommend using git-filter-repo, which should be preferred over git-filter-branch (older code snippets often use it).

Use git-filter-repo's --to-subdirectory-filter and --tag-rename:

https://github.com/newren/git-filter-repo#solving-this-with-...

[wdb]

Do you think this will speed up things? I tried the above suggestion and it's already for four hours to merge two repo's into one (3 years worth of git history)

[oftenwrong]

I am not sure; I don't know much about performance of git operations. Which step is slow? Have you figured out why? I am curious.