What is storagekitd?

I don't have deeper knowledge why this might take up so much RAM but this is what I found. You could also try to find out more about the process by clicking the info button in the menu bar. Do you see any connections to a certain program you are running?

Here they describe it as a part of the Disk Utility Program.

Open Disk Utility in Sierra or later (possibly El Capitan and earlier too), and watch in Activity Monitor for the appearance of storagekitd. This is the StorageKit daemon which runs as root and performs most of the work for Disk Utility. One reason that Apple has adopted this level of complexity is that many of the actions which Disk Utility has to perform require root privileges. Disk Utility runs in userland: in Activity Monitor, its user is you. To give it secure access to actions requiring root privileges, storagekitd is a helper, running as root.

On this website it is described as:

storagekitd is used by the StorageKit framework for disk state keeping and privileged operations. It is used by various clients in macOS. It is not meant to be invoked directly.

Maybe this helps to find out why it is taking up so much of the RAM. Do you have anything running that might be connected to disk utility?