nixos-install stuck after following disko quick start

I have referred to the following page: disko/docs/quickstart.md at 51e3a7e51279fedfb6669a00d21dc5936c78a6ce · nix-community/disko · GitHub
and used this disko/example/btrfs-only-root-subvolume.nix at 51e3a7e51279fedfb6669a00d21dc5936c78a6ce · nix-community/disko · GitHub for disk-config.nix

I have followed the steps, and i ran nixos-install, but for over 20 minutes I am stuck at building nixos-manual-html
I have used the simple graphic installer before and it did not take this much time.

What can be the problem here? I looked up the web forthis but cannot find anything.
This is a VM running 6vCPUs and 4GB ram (virt-manager) . CPU usage is consistently 75% percent