You're probably riding in pretty ideal conditions : very little walking required, almost no traffic stops, perfect weather generally?
Most Keo cleats don't make it pass 6~9 months in typical city centric housing locations that have plenty of traffic stops in my area. Most SPD-SL cleats last in the 12-24 months range as far as the local bike shops/riders feedback go. Like for like usage, the typical difference still stands in terms of durability. Except that in such (ideal )prolonged use, chances are the plastics deteriorate and fall apart before their wear rate differences can be told.
My own Shimano pair has lasted me about 25 months and its still got another ~30-40% life left.