I dunno, some Dragons can never be too big!

Unfortunately I have no experience with hero clix stuff, tend to avoid it like the plague.
I've been using Reapers smaller dragons as 15mm dragons, they fit in very nicely, I think I even remember someone using one in a post on this forum for a 15mm diorama with a knight. This one is my favourite
https://www.reapermini.com/OnlineStore/dragon/latest/02549.
Its a tad expensive, but if you want cheap, many are now produced in the Bones series, which may be worth a look. Don't have to strip them either!