The concept is fine.
Meeting members of the decemvirate when you're a low-level mook is weird and awkward, especially considering you already know everything you need to.
There were many skill checks. This was fine for me, because I was playing a rogue. Not so good for others.
There was a research scene. This is an optional subsystem that involves making a million skill checks over in-game hours. Woo, the excitement.
The biggest monster showed up during this research scene, and we got no warning so we didn't have weapons drawn or shields equipped. The monster did not have to spend actions equipping its weapon and had high initiative. We had predictable (unshielded) level 1 ACs of 18, and it had +12 to hit (for d12+5 base damage), so it dropped the best fighter before they got to act. After that it was an extremely predictable TPK.
What's bad about this is not the TPK. It's the utter predictability of it. It showed up with no warning, had high initiative, and had a lot of HP. Plus it had a 1/4 chance of critting and a pretty good chance of insta-killing anyone it did crit. And what's really bad about all this is that level scaling is built into the game mechanics. It's not like a PF1 random death from a mook with a greataxe critting - the monster just isn't down-scaled if you're level 1. The system arithmetic is very predictable, as are the consequences.
Conclusion: the boss needs some level adjustment, a round's notice that the encounter is coming so the martial characters don't waste the first round drawing weapons, and maybe a smaller weapon. After that the scenario could use some tweaking on the skill check DCs.