I still remember I successfully killed the commander the very first time I started this game - this is hard to forget, as there is an weirdly named achievement for killing that commander, called "Devils in the Details" - I got the achievement when I had barely started playing BG3.
I remember I needed time to kill him and other enemies.
It took time to
. fight 2 batches of enemies
. kill the fighting duo (both of them - one after the other)
. check out a number of items and bodies lying around,
. hoping to find something that could help me kill.
Even 15 rounds were not enough!
but I understood I had to leave.
I think a 15-round timer is a perfect compromise for a first-time player or any newbie like I was.
Later, on Tactician mode, I learned the hard way that I have and can only have 6 rounds to get everything done (listed below), otherwise any of my companions may have to die - for role-playing, all my companions must not die.
. steal the great sword,
. loot the void bulbs,
. check out every corpse,
. pick the oil tanks,
. deal the killing blow to the illithid that would later offer to kiss you in order to heal itself on your cold body
My opinion is:
. let the player decide when to leave.
. the current 15 round timer is perfect for players of all experience levels.