Release-upgrade 20.04. to 22.04.3 questions

[Bo Berglund]

My Linux server runs this now:
Ubuntu 20.04.6 LTS (GNU/Linux 5.4.0-164-generic x86_64)

I intend to upgrade to 22.04.3 LTS and I have a few questions.

1) How much additional disk space will be required for the release upgrade?

Currently I have this (it is running virtual below VMWARE ESX):
$ df -h
Filesystem                         Size  Used Avail Use% Mounted on
udev                               438M     0  438M   0% /dev
tmpfs                               97M  1.3M   96M   2% /run
/dev/mapper/vpnserver--vg-root      28G   19G  8.3G  69% /

and (output for smaller items removed):

$ sudo ncdu -x /
    9.3 GiB [##########] /nfs
    4.1 GiB [####      ] /var
    1.8 GiB [#         ] /usr
    1.6 GiB [#         ] /home
    1.3 GiB [#         ] /lib
    ....

So there seems to be 8G free on /
Will that suffice or should I try to shrink the installation somehow first?

2) Will this be a lengthy process or can it be done in say an hour or less?

TIA

-- 
Bo Berglund
Developer in Sweden