This is how we determine memory usage. We have rounded up the numbers to be on the safe side, and also because (after all), this is a round update. ;)
0.6 MB just to boot + 0.5 MB for loading ROM modules + 0.9 MB for free memory.
Of course, in a system with a physical Kickstart ROM, 3.1.4 will work nicely with just 1.5 MB of RAM, but as said before, we needed a blank statement that will work under all systems, so 2 MB is a good bet to stay on the safe side.
The most intense, OS memory-hungry process is when you run the 3.1.4 Installation; the installer's script compilation procedure is what eats most RAM.
Taking it to the extreme, a system which has been installed using UAE can be transferred to an Amiga where it could even work with just 1 MB of RAM, provided that the Amiga has a physical Kickstart 3.1.4 ROM chip installed.
