I think answering "will it be as good" is a really hard one to assess because of other factors outside of the defensive players themselves.
- A new system, two new coaches, and a new DC. Could be good, could be bad, most certainly changes expectations and results. I lean to the optimistic side and what I'm hearing about the players thoughts of Semore (that they really like his strategic mind, game prep, and defensive design). It suggests it should show improvement over Gregorak's external style of brute force, being tough, being a wild animal, etc...
- The offense. If this offense can score 7 to 10 more points per game or even have 3 to 4 more minutes of TOP per game that will work wonders for the defense. Less time on the field as a whole, hopefully fewer games that are tight and in need of multiple defensive stops, things like that. The offense should be able to improve over last season, if so that'll help take the pressure off the defense as much and keep them a little more fresh in the games.
That said... losing 8 starters is tough... I have a feeling that the first half of the season we'll see some adjustment. For the coaches and the players and it'll probably have people running to the message boards bemoaning the new system, new players, new coaches. But, over time, I think it's going to improve and it may be pretty damn good by the end of the regular season and into the playoffs. The 2016 defense I'd guess will not be "as good" statistically in many categories as the 2015 defense at the end,( stack up PPG, YPG). However I think other factors, such as an improved offense, will probably help and make us think a little less about the defense as a liability. Additionally if the defense keeps getting better and is playing at a top level in Nov/Dec... that's where it'll matter.