I have quite powerful server: 24 cores, CPU 3.33Ghz, 48GB of RAM. I am cloning three separate containers at the same time however and it takes 10-15 mins to clone one container. However, from task manager we are able to see that quite less resources are used.
Clone operation depends on the size of the container and how many files are located inside it. So, if container has very huge size, it will take a while to clone it.