Probably your players have low passing skills, or dunno.
For many times I play with long passes + counter attacks, but I dont remember my team ending a match with less than 85% completed passes.

But listen. If with this low passing % you are getting good results, you shouldn't get worried about it ^^. In the end, what matters is to win.
If you are getting bad results, maybe you should try to play with short passes, turn off your counter attacks and play without a straight attack mentality.