I think that's extremely realistic.
Plus... d-line is back and more experienced. Linebackers are back and more experienced. It looks like the losses in the secondary are heavy, but since 2 of the 3 guys didn't last the season, really, we're talking about replacing Iffy and seeing some improvement out of all of the guys that were pressed into action. It seems realistic that with an offseason to get ready, both physically and mentally, that they'll be better.
I'm pretty bullish on the defense in general. And yeah, they'll be helped a whole lot by having an offense that doesn't outright suck in historic ways.