I am worried that 16 hours won't be enough to run even 75% of KotS though. How many hours have people put into this when running it?
We've gone six sessions (averaging about 5 hours each), so far, and we just completed the encounter with the Zombies, Ghoul & Homunculus. I think we're about done. We're a large group, though, 7 players, with no more than one missing per session, and the encounters are expanded to match, which surely slows things down.
I'd suggest that a lot of encounters could be done away with: the second kobold ambush, the archaelogical dig, and all the cavern encounters, for instance. The undead encounters leading to Sir Keegan could be trimmed down to only one, too, and the Hobgoblins, likewise.
Of course, you still have to get your part to the right level to face Kalarel.
You could skip the Kobolds entirely, start your party at 2nd level, and send them straight to a slimmed-down Keep.