I'm on 16GB 2800MHz, the only time I saw my RAM usage reached 15GB was when I had a Celsys Clip Studio project opened (with lots of layers), Photoshop CS5, Opera browser with dozens of tabs, music player, explorers, and lots of image references opened, while installing game from Steam and playing game at the same time.
I was tempted to get 32GB kit at that time, but apparently installing game from Steam requires LOTS of RAM, outside that scenario (installing game from Steam) I hardly ever reach 14GB even with all my project opened and game running. Instead of 32GB upgrade, maybe an additional 1TB SSD or peripheral upgrade is a better choice for me. Or maybe I'll just wait for DDR5 later alongside with new CPU.
IMO, it really depends on what kind of productivity you're doing and what you use your PC for.