Fast, cheap, wireless data transmission with Raspberry Pi
You can go for LORA but that's normally more expensive.

2.4NRF ... not sure if it can reach 30 meters (depending on obstacles/walls). Maybe with an external antenna. 

433/800/900 MHz RF is mostly having a longer range, but a little more pricy (less than LORA).

I only did tests with Arduino and nRF with quite high speed (I think 2.5 mbps) and got a reasonably accuracy with about 6 meters and a wall in between. If you need less speed, you can go (much) further than 6 meters.



60 bytes * 8 bits/byte * 15 packets * 10 slaves = 72 kbps. This is a reasonably low speed (even for RF). So you can use expect to get higher distances, but you have to do tests to be able to reach 30 meters (with obstacles?) with nrf24. I didn't know about the 1% restriction. Btw, wireless microphones use sub 1 GHz transmitters/receivers and that bandwidth is much higher.