bitcoin QT can sometimes use upwards of 1 GB of RAM.
With some custom settings to limit what gets held in memory, you could get this down to less than 10MB, but it would require a fair bit of work.
Whatever work is done must not slow down the speed at which the node works. You would be doing the network a disservice if your node took a long time to validate and relay messages and blocks because of your low memory footprint and under-powered CPU configuration.