iOS 15 works well for a beta so far but as with most years some banking apps aren’t working. I’m seeing a lot of people hassling banks to update their apps now but even though it’s a public beta app makers have no reason to rush through updates to help you. This is especially true with banking apps, I wouldn’t want my bank to rush out an update.
In using the beta any third party apps you rely on might break, please don’t hassle the developers.
This is the main reason I keep my iPad Mini on the current public release of iOS 14, so I can still do my banking. If you rely on any third party apps that aren’t working then please use iOS 14. I’ve not noticed any other third party app types failing to launch on start up but if you find any let me know.