I'm actually using Desmume, but got some really hard lag when 3D models are on the screen (in the map expecially)

No$GBA runs better but has a couple graphical glitches. You could try that.

I know I am late but sadly Desmume is the only allowed emulator.

Also, Desmume has settings like frame skip or whatever to reduce lag. It even let my garbage laptop stream ds games.