Akonadi is a storage service that certain KDE programs use heavily. I only use the KDE windowing environment and I don’t use any of the applications in KDE, so akonadi was just wasting RAM and potentially CPU.
So to disable it, set StartServer=false in .config/akonadi/akonadiserverrc:
It might still load if you use KDE-dependent apps, or it might cause your system to blow up. But that should do the trick.