Try creating a Favorites list, then edit it to delete Sites that are not within the area(s) you will be listening from. There are not that many talk groups in the system you quoted, so that should not be an issue. It is probably the large number of sites in the system that gave you the warning message.
You may not be hearing them if they do not chatter too much when there is not a storm. My local power co. PEPCO, may transmit only 4-5 times an hour during the day when they are just doing routine maintenance, to open or close power blocks. I think dispatch may be done via MDT.
I usually hear the most talk when they have lines down due to storms, I don't monitor them any more during other times.
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I leave the favorite list active, I just uncheck "Utilities" from system types to stop monitoring