Smooth running video https://www.youtube.com/watch?v=plh9OGel-lM does 60 fps on emulator. Real hardware video shows 15-20fps in a small room and author himself confirms its unfeasible for anything more complicated (~8 minute mark).
15-20fps is a pretty normal framerate for many games on the real Nintendo 64 hardware, especially the later ones from Rare.
The PAL versions of Zelda ran at 15-20FPS even on emulators in the PC. Yet they were pretty playable.