It's worth looking at if you are working with nrf52. It has a fully open source Bluetooth Low Energy stack, down to the controller which is attractive. Unlike FreeRTOS adding various modules doesn't cost anything.
Not sure where you got the 16-32MB quote from, but if you run checks on the code size the kernel is ~5 KB and a fuller RTOS (without secure bootloader) with the BLE 4.2 stack is ~100 KB.