Until recently I worked with adults with special needs and we used to do bingo evenings for them. It was slow and we had to repeat everything several times, but they loved it. We had to have an extraordinary amount of comfort breaks too, but it didn't spoil their enjoyment.
Now that would seem to get very irritating to repeat everything 150 times. I wouldn't want to be the bingo caller. Maybe after practice with the players they will not need it repeated 150times.
I've worked in special need homes as well as elderly peoples homes, but have never called bingo in either of them. I have got a Btec national diploma in performing arts and from what I learned there as long as you speak slowly and clearly they should be able to follow. Also repeat the number a few times before moving on and check with your eyes to see that everyone is with you before you carry on and you could always ask if everyone is with you.
You are welcome I see what you mean about the PA unfortunately there is nothing you can do about that. The other thing you can do if there are some people who have real struggles keeping up is have an extra member of staff walking round the room helping those who are struggling, but that would only work if you have extra staff and in elderly homes that usually doesn't happen. Maybe you could ask some of the more abled elderly members to sit next to those who struggle and help them.