Looking at the scoring defense from 2014 and comparing it to 2013, there were 2 teams (West Virginia and SJSU) that were >100 in scoring defense in 2013 to the 80's in 2014. On average last year, teams ranked 1.52 (not really unexpected really) spots lower than they did the previous year with a stdev of 36.3 spots better. One team dropped 105 spots (Bowling Green) and one team improved 83 spots (Air Force). Overall, 28 out of 127 teams improved by 30 spots or more from 2013 to 2014.
Any given team has about a 20.1% chance of improving 30 spots or more.
Any given team has about a 28.8% chance of improving 20 spots or more.
Any given team has about a 39.0% chance of improving 10 spots or more.
So while optimistic, not wildly out there.