As a new player, running through the Praetorium dungeon was the worst

[KisaiTenshi]

I did Castrum Meridianum and The Praetorium back to back in Undersized party mode, with the cut scenes on, and not clicking through any of the dialog (auto advance):

Castrum Meridianum
Exact time: 44:33 (from Instance start to Exit), Timestamp 41:48

The Praetorium
Exact time: 62:16 (from Instance start to Exit), Timestamp 58:08
https://youtu.be/EuTNvt5jyVw

So to go back to the point of the original post, In order to watch all the cut scenes, it does in fact take twice as long for the Praetorium.

Also, got pinned by Nero on that run, which meant that I had to defeat him using Aero II, which probably dragged it out another minute.