Audio Audio Source doesn't play properly when you give more time to Microphone.Start()

Hello there.

I'm doing my own Microphone manager.
I already have everything to do that, but right now, I have my function to take the spectrum data of my Audio Source, but there is something wrong because if I initialize Microphone.Start() with one second and I play my Audio Source its spectrum data doesn't take time to get it, but if I initialize Microphone.Start() with 15 seconds that's gonna take 5-10 seconds of delay to get that data.

I need those 15 seconds of clip because I send that data to Google Speech to Text.
Is there something in Unity to move or in my Audio Source?.

I was thinking to combine each one second of samples length to a new float[] data like sum, but I don't know.

Thanks!!.