The Curse of Strahd group I was in started at 3 and ended up around 15 (which is beyond the module, but the DM homebrewed some stuff). Currently in a Dungeon of the Mad Mage campaign that the DM says will go to level 20...we started at 5 and are level 9 right now. But, yeah, most adventures cap around lvl 12 without adding homebrew. I think that's about where the Call of the Netherdeep campaign ended that I DM'd...I did start them at level 1 because it was my first time DMing, so I did a small 1-3 module first to see if I could hang.
In 5E, characters are near-impossible to kill at the high levels, so I think that's part of the reason most campaigns aren't designed with those levels in mind, but I am excited to finally get a character up there just to check it off the list. Currently playing a Rogue...combat is boring with basically one attack per round with the main objective being to get sneak attack damage. If I miss or can't get sneak attack, it really feels wasted. But the roleplaying with this character has been really fun and I'm looking forward to the higher tier abilities that I'll never ever get another chance to try. Definitely going back to a magic user in the next campaign, though.