Because LMDE runs on Debian, you won’t have the extra fixes for audio that ubuntustudio offers (mint runs on the same repos as all ubuntu flavors). Also, LMDE is debian, and their packages are older.
Regarding ram, reaper uses way, way less ram than any other daw, because it’s the most optimized of all. The creator of it, who also did winamp back in the day, is known for his optimization black magic.
I use Mint with Cinnamon with the Cinnamenu menu (instead of the default ugly one). I’m able to make Mint to start up at 700 MB of RAM. On my fast desktop I have Debian Testing with Gnome 47, that one starts at 1.5 GB of RAM. I’m thinking of using Mint there too.