I think that's just the Docker for Mac client (and Hypervisor.framework). I think the disk I/O performance was bad, the last time I used it was for Node.js/Postgres about two years ago. I was able to really speed up the integration test suite by disabling fsync for Postgres.
If you were running native Linux it should be a lot faster.
Even on a top of the line macbook pro that shit chugged.
And the laptop would get HOT.