@Elaine701
I haven't used other platforms, so I am not sure of the fees on those, but one thing I do not like about the Airbnb pricing system is that the guest fee is not a fixed percentage, but variable.
I do remember back in 2016, when I started hosting rooms in this house, Airbnb said it's guest fee was typically between 6-12%. However, I don't think I've ever seen a guest charged as little as 6-8%. It's usually on the higher end of the scale, or even more. I'm rubbish at maths, but you can see that the recent example I gave is more than 12%.
Now, this is a newbie guest on his first stay. It is rumoured that Airbnb charges lower fees to newbies to draw them in and higher fees to regular users whom they feel they have already hooked.
I have heard that some guests are being charged close to 20% these days...
So, the 15% host pays option you have selected does make sense. At least you know what the total is going to be.