The Colts were one of the most improved defensive teams last year. They went from being near the bottom of the pack in every statistical category to near the middle. They went from being very bad to average. A jump like that is truly significant. The Colts certainly seem to think so.
They think that jump is so significant, that they want to bring everyone back from last year. They have re-signed several defensive free agents to keep the band together. Margus Hunt, Pierre Desir, and most recently Clayton Geathers all have new deals.