That sounds like a lot, but I dunno how heavy the standard large bag of candy is. You must get a hell of a lot of trick-or-treaters usually.
Two or three bags is enough for us, which leaves a portion of one bag left for us to dig into. But this year we had only a small amount of kids come out, and fewer to our door. Likely a combination of the weather + the kids having mostly grown up in this neighborhood.