Expected native build times on an RPI4?

Hello All,

A 'make -j3 buildworld' of a freshly checked out -current tree
took over 15+ hours on an RPI4 before eventually running out
of space (/usr/obj had reached 7G by then).

The CPU(s) ran at a top speed of 1500Mhz during the build,
per 'sysctl dev.cpu.0.freq'.

Even so, the build hadn't managed to cross the 'building
libraries' step.

I'm wondering how best to provision for building -current:
how long does 'buildworld' take on this device usually, and
how much disk space does a build of -current usually need?

Thanks,
Joseph Koshy