I was congregation Secretary when the change to 15 mins came through and so had the record cards. I would say previous to that that I counted an hour for all the old shut ins unless they went into a nursing home or are home and would often put them down for an "hour". A couple of scrupulously honest ones would say they didn't get anywhere near an hour and weren't happy to count a full hour.
I would say that in our cong of about 85 at the time it allowed one or two to be counted over the years for a year or two longer than they would have done before.
And yes - Secretary's and other elders will put down 15 mins for residents of nursing homes without ever speaking to them or knowing they if they have done any "ministry".