The challenge for the radio communication is two-fold:
1) I need to send up to 15k samples (12-bit ints) every second.
2) I need to send 15 samples simultaneously from different devices without worrying about protocol or collisions -- radio is not my expertise.
The two options are the NRF24L01 and a RF4432 module.
The latter has several hundred MHz of adjustable frequency, but I can't actually use the entire frequency range on a single receiver, nor can a single SDR module cover the entire frequency range. If the frequency range was more limited, I could maybe use an SDR hooked up to a Raspi or a BeagleBone to act as 15 receivers via frequency analysis -- an FFT, or something that can decompose a signal into its frequency components.
With an NRF24L01, the frequency range is significantly more limited, and a more crowded area of spectrum is used, but each module put into received mode specifically supports 6 chips, each on a different. That support requires that only one of the 6 transmitters can send at any given time. Since collisions are pretty much guaranteed in this project, this may not be a feasible solution.
Note that both of these problems vanish if I can have the controller chip, not the sensors, do the radio operation. Essentially, this is centralizing radio communication, and eliminating Challenge #2. However, that requires limiting which microcontrollers people can use -- a limit on free will I'm less comfortable with. Limiting sensor choice seems like it would be more acceptable across projects.