for a real artifact.

I got the feeling that achieving a result of 15 days was very easy.

That's exactly how it was! It was easy to achieve 15 days. But it was impossible to achieve less.
Only the second criterion could have influenced the outcome.
And even with that, it wasn't that difficult... the only catch was with the Pirate... that's all...
Since I didn't notice the Pirate, I even created a third criterion for myself - gold ;) (Mephala had higher starting parameters than the others (except for the Pirate, whom I didn't notice), and she was good, so no troops were required for the altar).
If I had noticed the Pirate, of course, the gold would have been at zero, as he is a neutral creature, and in that case, I would have spent everything on building Castles and buying troops, in addition to gathering experience from monsters on the map and artifacts. I would also have tried to figure out how to get the computer to switch to the Pirate on the transition to the next week so that before buying, I could defeat him with several heroes... that would have been a bonus...
Of course, in that case, I would have had to play around with the computer, taking and giving the Castle back without killing it...
I would also have had to struggle with the refugee camps, generating not only mages but also archangels