My post here is a bit off topic … But … anyway … if you like the idea of booting GNU/Linux off of an external device, you may wish to consider in the future not using an external HD, but instead use an external SSD (ie a nominal SSD bought off of the market, housed in an SSD enclosure) for your openSUSE.
USB-3.1 SSD enclosures are incredibly inexpensive … and even the price of Thunderbolt-3/4 external SSD enclosures have drastically dropped in price. ( obviously most the expensive is the price of the SSD if a large capacity SSD).
I purchased a dirt cheap USB-3.1 SSD enclosure and thus far I am happy with it. Fortunately I had some help in setting it up … and I managed to find a work around for a premature going to sleep issue.
I posted about his here:
Of course this is pretty new for me - and perhaps with time my opinion will change, but at present I am reasonably impressed and happy. The boot times I am getting are a fraction of yours (albeit our systems are likely very difficult). For example I am still using EXT4, although I do not know enough how relevant that may be.