Here is what you should be aware of iOS 15.4 upgrade, besides losing more battery as per Apple this is normal. But I wonder if it's just Apple just being sloppy when upgrading their software and refusing to fix their ongoing battery life problem with their devices.
Here are some recommended fixes if you are trying to find solutions to your problem.
Here are some good tips to troubleshoot Window freezes. This always requires lots of patience, you need to wait until things free up so that you can save your file and continue.
Then try Cntrl + Alt + Del and wait for the screen to blank before selecting task manager. In task manager click more details, if visible and any non-responsive program should be highlighted and you can attempt to close it or try to recover it. This will take you to a detail tab, where processes are listed with more information on their status.
Right-click the non-responding thread and choose to Analyze the wait chain. This waits to use resources being used elsewhere which can result in the program freezing.
And Sometimes the Task Manager appears to have no effect. In these circumstances, you may be forced to reboot.
Chrome is taking its OS to a new level by reviving old hardware using the Chrome OS Flex. Not only will you bring back old hardware to use, but can extend its lifespan.
Anyone looking to extend the lifespan of their equipment should give this software a try. It's a worthwhile consideration.