I think Green is a better fit for the role honestly, he has more size and athleticism than Harrison.
As to the latter.... to be clear, I think most 2nds willing to take a two-way have less upside than our current two-ways, or at the least that having already put a year of development into the two-ways, and the staff liking them means you should keep them rather than gambling on someone new who isn't clearly better (if they were they wouldn't be taking the 2 way).
as to the 12- (Turner, Lee, Ellington, Belinelli,Chandler, RHJ, GR III, Moore, Galloway, Korver, Mudiay, Ilyasova) If I missed any of those guys, I also would rather Batum on the minimum once he's officially waived.
Overall though, construction wise, I think it makes sense to let Green hold the 15th spot to keep things nice and clean while you look for trade and buyout options throughout the season.