It is painful, but sometimes the only way to solve performance problems is to perform a factory reset. If you have gone through all the other possible paths, including resetting all the individual settings, then this is necessary. A factory reset erases everything on your smartphone.
First of all, back up all your data. This will ensure that applications that use cloud services have been synced recently, as well as make a copy of any photos or application data that are local only to the internal storage of your device. To do this, go to Settings> System> Backup.
Then in Settings, go to General Management and Reset to find the factory data reset. You will receive a reminder that you are about to lose everything that is stored.
Your device should now have the problem fixed. Be very careful about which applications you install, and how you configure the device.