Hey DenebQuarlo,
Thanks for the reply, additional info and screenshot. We appreciate it!
If you start your Mac up in safe mode, and test with keyboard dictation for awhile, do you still see the memory usage as before?
Keep in mind that with safe mode your Mac will take longer than normal to start up. Plus, you may see some flashing or unusual display behavior. This is expected, and by restarting normally you'll exit safe mode.
Use safe mode to isolate issues with your Mac
After restarting normally, see if the memory behavior is still the same. Safe mode also does some system checks, so it can clear up some funky issues.
Testing with another user can also help to isolate this issue further. If you need to create a test user: How to test an issue in another user account on your Mac
Thanks!