I haven't seen that behavior before... I have a client that has been running the global network for several days in a row without restarting on an 8-core machine, and when idle it is using around 700MB of memory. Most of that is cached item and spell data. We also run it in server GC mode, which consumes a lot of extra memory to improve throughput.
It is certainly a CPU and memory-intensive program, though when idle, it is probable that were your computer to become busy it would release some of that memory.
Next time I fire up my cluster of linux machines I'll try connecting to one to see how much memory it is using. I usually run ubuntu 16.04.
You could also try manually configuring it to use workstation GC mode, which would significantly reduce memory usage, but might slow it down a little. To do that, open up amr.runtimeconfig.json in both the AskMrRobotClient and AskMrRobotClient/version425 folder and set System.GC.Server to false or remove it entirely:
Note that if the client auto-updates, you would need to manually change it in the versionXXX folder again.