You're correct, it fits between episode 16 and 17. The end of 16 teases that there is something sinister within SHIELD but not anything specific (even the source of the tease is a mislead). Episode 17 technically takes place at the same time as Winter Soldier, so one spoils the other either way, but the intention is obviously to see Winter Soldier first. The show spoils the ending of the big movie, but watching the movie doesn't spoil what is set up to come in episodes 18, 19, so on.