I'm concerned that all my recent visits to my child have been for only about fifteen minutes. I arrange to visit in advance and go with the intent of staying longer. I'll just get started playing a computer game which "Jesse" likes and the caregiver will say, "Oh, Jesse needs to change to his Cub Scout uniform as we need to leave in a few minutes." The next time it will be something else which cuts short the visit. Sometimes she apologizes, but basically she seems to think this is okay.
Yes, I would be concerned too if I could see my child for only fifteen minutes a month! It also raises a question of whether the caregiver is manipulating circumstances to make the visits short. At any rate, the next time you call to arrange your visit stress to her that you want to set a time when there will be no problem for you to stay an hour—at least 45 minutes.
You may need to remind her that you are required to make these visits and that they need to be more than token contacts with Jesse. In fifteen minutes, you barely have time to learn that he appears okay. You can't observe much about how he is relating to other children in the home or how he is relating to the caregiver. He isn't warmed up enough to talk about school, other activities or anything that might be troubling him.
If a guardian ad litem happens to be working on a case where visitation is needed several times a month, then shorter visits part of the time may be adequate. Remind the caregiver that occasionally you will visit Jesse at school or daycare if a younger child. Likewise, if the caregiver is not a parent then some of your visits can be to observe his visitation with the parent. When your monthly visit is at the caregiver's then do stay about an hour most of the time.