Mine is up to 26G for now with some images:
ls -alsh ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2
55331840 -rw-r--r-- 1 jmaitrehenry staff 26G 12 Apr 23:07 ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2
```