If you plan to use an emulator to speedrun this game then I would recommend using citra, I've been informed by another moderator that an I'm allowed to link it but you must go by your own terms acquiring the game. Citra is the most worked on and stable 3ds emu at this point and I can personally confirm that Tekken 3D: Prime Edition works alright on the emulator if your specs are good enough to run it (Compare my video to SlawPro's for an example). The emu is constantly being updated so hopefully the game will be more stable for lower specs.

Emu Link https://citra-emu.org/game/