I had a Vagrant VM on my other laptop that I wanted to convert into a Qubes AppVM (StandaloneVM).
The disk was lazy allocated 40GB but only using about 1.3GB within the guest.
The underlying disk of the Vagrant VM was a .vmdk. A lot of guides online talk about compacting VDIs, but I had to convert my VMDK first, I couldn't compact it directly.
Here's how I got it into Qubes.