The initial updating process after new installation is slow because of the large number of updated files, and updating sometimes hangs in the GUI updater (libreoffice-common is the most common culprit). The weekly updates, on the other hand, are usually quick.
Solus runs fine in VirtualBox. I ran Solus in VB for several months while testing it before adopting Solus. Solus updates and runs normally in that environment, and I had no issues at all after installing the usual VB extensions/additions to interact with USB ports and so on. If you are looking for a shortcut, you might try the OSBoxes VDI rather than trying to build your own. The pre-built VDI is easy to install in VB and works. I use VB and OSBoxes VDI's to look at distros from time to time.
I don't have any experience with trying to clone VB and VDI builds to an SSD to create a portable build of Solus. As I understand it, VirtualBox is not portable because it installs drivers and system hooks, so VB would have to be installed on your office computer. I am aware that software exists that claims to be able to create portable VB and/or Linux instances (Portable-VirtualBox, OS Launcher and so on), but I've not had any experience with them.
It may be possible to swap installs between computers, so long as the computers are all reasonably generic (standard processors, onboard graphics and so on), all have similar specs, and all have SecureBoot disabled. The reason I think this is that I built a stand alone external SSD running Solus. The external SSD contains the boot sector and the Linux Boot Manager. I've used it on several computers without problems. It seems to run like a "live" USB but is persistent. It was a nerd/geek project rather than an attempt to do anything practical, but it seems to work okay.
Building VB and/or portable instances seems like a lot of effort just to be able to run Solus during work breaks. Why not take your laptop to work and boot it up during work breaks?