I agree with Chef on this one. Those two cabs are just so different in every way, efficiency, voicing, cone size, tweeter design/crossover, and while it 'might' work, a betting man would take the bet that it would be 'strange'.
If you kind of dig your 115L+, I would highly recommend getting a second one of those. Your low end would extend a bit through coupling, and you would have 'more of what you already like'.
If, on the other hand, you aren't digging the 115L, I'd make a clean break. You obviously aren't 'weight sensitive' with that head. One of the fEarful 15/6's would probably really float your boat with that head, if you are looking for more low end, and more clarity through the upper mids.
IMO there. Jim Bergantino is getting ready to start shipping the new HD212. Not lightweight, but basically a double HT112ER..... that, with a DB750.... as Tom Bowlus says 'boy howdy'