Thanks AB2012, very informative post as usual.
I was not actually trying to imply that you should test everything, merely curious as to how one could go about testing their own libraries. I think I have enough to go on now, thank you.
Whilst I don't have anything to test them against, I have noticed a few games gog games that seem to have very long start up times indeed, if it is of any use to you or others.
As you suspected, Deus Ex Mankind Divided takes ages to load up (I have just finished playing this in fact). I had actually noticed this before this thread but put it down to me having an old machine. Usually pressing escape, return, space etc can get you through the initial splash screens, but not with this game. Probably the ghost wrapper, though I can't confirm for sure.
Now that I know what I am looking for I suspect another two games that I currently have installed: Prey and Xcom (fireaxis). Can't be sure but they fit the startup times you mention. Again. never really gave it a lot of thought until I saw this thread. I am using the long war mod with Xcom though so even less sure on that one.
Anyway, a far from ideal situation, let us see what gog intends to do about it.