@Hyena, what image are you using for your RPi2 (Raspian, Debian, etc.)? I’d need to check but I’m pretty sure that by default the Nu build process has a lot of the debug flags turned on. Turning them off would reduce the build process memory usage.
I’ve never built for RPi but I know that compiling Bitcoin and Peercoin (along with Nu) require me to enable a swap any time I’m spinning up a small DigitalOcean droplet or it will run out of memory. It could be that the Satoshi-client derived wallets aren’t optimized (maybe because of the libraries used, like Boost – I’m just speculating at this point).
Anyways, ultimately it would be nice if we could cross-compile the ARM builds on beefier machines and then shift the binaries over to an RPi, primarily to avoid the ultra-long build time even if memory wasn’t a problem.