It's probably more about the .ifo files than the size of the dictionary in total, but I suppose their size is highly correlated.
I don't know what's usual among users as we don't collect statistics or anything, but I would imagine that is indeed unusually large.
The biggest dictionaries I can think of from the top of my head are the GNU Collaborative Dictionary and XML Littré, which top out at a little over 30 MB iirc.