Just personal opinion but considering that most users can make do with 8GB RAM, only if someone does a lot of video editing, has several VMs running in the backgound, is doing 3D CAD work, etc and all are being done at the same time, then 16GB might be the way to go. Here's some other forum threads that may give you some other perpectives.
How much RAM is too much? 32gb? 64gb? - AnandTech Forums
16GB enough? or go for 32GB? - Hardware Canucks
Do I really need 16GB of RAM?
1600Mhz 32gb vs 2133Mhz 16gb - Overclockers UK Forums
Have you tested your machine in your
real world environment to see exactly what benefits or problems you have when running 16GB with lower latencies vs. 32GB and higher latencies? Whichever setup gives the best performance or most noticeable improvements is what I'd go with.