iPhone malfunctioning

after updating to os 15.1, my phone started constantly giving an error that there is not enough memory, even though free + - 6GB. because of what I periodically cannot use mail, camera, watts app, gallery is defective. All applications are not stored in RAM. every time you have to start again. VK applications are unstable, instagram feed does not load (the problem is in the OS, and not on the part of the application developers). The phone just reboots. There were no such problems on iOS 14. As soon as I installed iOS 15, small lags began, but after installing iOS 15.1, the phone stopped working correctly at all.