[D] How can Elevenlabs return a response so quickly?

AI based tools, like Elevenlabs for TTS, can return an API response with constructed audio in <1 second. How on earth do their models return so quickly?

For comparison, TortoiseTTS returns the audio for a sentence in minimum 15 seconds.

Obviously they have VC funding and hardware. They probably have slimmed down models, but the speed of their response is insane.

api audio comparison earth elevenlabs funding hardware machinelearning returns tools tts vc funding