I'm just curious what people got out of the module going into HotU. Tempted to skip a bunch of side content but don't want to lose the benefit going into HotU.

When I finished SoU I was level 17 but I started as a new character for HotU. You automatically start with level 15 and I finished the game level 27. Well if you create a new character you start as level 1 with enough experience for level 15. Start of HotU was very easy for my Druid in hardest difficulty.

Typically I finish SoU somewhere between level 12-14, with the biggest variance coming from whether I take a henchman or not (which siphons off much of my XP)

The way the XP system in NWN works, I wouldn't worry about being a little bit behind. The lower your level, the more XP you'll get for defeating the same enemy, so the system automatically plays "catch-up" if you do fall behind. So long as you're strong enough to survive you'll quickly get enough experience to catch up to where you should be.