Sorry for the delay. Don't spend as much time as I'd like to lately on the fun stuff.
1518 isn't a typo. I didn't notice it wasn't in the db
Generallly, it would be a good idea to try any of 1509 thru 1519, but the two I mentioned should be good. Be aware that usage is different in the snow months; in construction months things can be different.
Under your mention of county roads, I believe the 156MHz freq may be the only correct one. I haven't monitored them on anything lately, but thought the 33 MHz was no longer in use.
The 6181 talkgroup is not Berrien County, but MDOT. Not sure of exact usage, area or designation.
Berrien County Road commission is not using MPSCS, with the (rare) exception of a supervisor unit or two on the 11COM tg's