I’m curious as to how taxing PiAware is on a Raspberry Pi 2. I am considering building my own PiAware receiver and trying to determine if I need to dedicate a new Raspberry Pi to the receiver of if I can just add it to another Raspberry Pi that is running a VERY low power application. The Raspberry Pi 2 I was considering using currently has a GPS HAT attached and functions only as a Stratum 1 NTP time server. It is running Raspbian Jessie Lite.
The amount of CPU it uses varies depending on how much traffic there is in your area. It will be just fine to run on an existing NTP server, though.
I have dump1090 and dump978 with Pro dongles running on an RPI2 with a GPS unit(running as a stratum 1 NTP server) with no problems. Dump978 uses a lot more CPU than dump1090.
I have seen RPI1s max out with great locations and antenna. My RPI2 and RPI3s run fine with STD dongles. The airspy overloads my RPI3 doing nothing else, from time to time. Maybe the new airspy-mini will be better. I also have a miniADSB on its way. I will order a mode S beast when they are back in stock at the end of May.