How to make provisioning of tier2 VMs faster

While I am sitting and watching provisioning going extremely slow (almost an hour going here, now waiting on the step of sudo tar -C /opt/ -Jxf qnx700.tar.xz), I thought it would be nice to have a ticket listing what we could fix. Please comment with your suggestions.

 EDIT: possible areas for improvement

• Use Zstandard instead of slower compression formats
• common/unix/install_protobuf.sh seems to take long
• Keep the read-write qcow2 VM image on the local SSD instead of the NFS share, until provisioning is fully complete
• Do not compile from source, but precompile whatever is possible (for example qemu is being re-compiled on every provisioning)