It's less to do with texture memory and more to do with GLSL implementation...
For now you should be able to rebel against the bad default and set
to get something that (hopefully) works.
OA doesn't support whatever debian downstream does for an engine (we only support this). I'm assuming it's forcing that new unfinished default OpenGL2 renderer - which looked completely broken last time I checked on a Pi3.
Doom's a trustworthy landmark game for anything DOS. Chocolate Doom shouldn't render it irrelevant (it's still not quite dos doom perfect either)