Sounds like you have a lot of stuff running in your device background.
1.) You can uninstall any apps you don't use.
2.) You can manually clear out your device caches by Opening Settings then Apps and go to each one by long pressing and clicking clear default.
3.) You can install CC cleaner app to do the job for you. Also you can set it up to do that on schedule intervals.
4.) I would try the CC cleaner app first and if your device show any improvement after running that application.
5.) I would troubleshoot the small reasons why my device is running slow before I would even think about trying to install a custom ROM or rooting it.
6.) You can also disable some bloatware\ pre-installed apps running in the background from App settings.
