Every samsung galaxy note phone I have owned sincece the first note has never experienced a slow down , because I have aleays maintaned my phones like you would with a computer , and checking for and removing resource hungry software etc ,
My galaxy note 4 was running temperature af anywhere from 45 to 80 degrees celsius and often would reboot because of temperatures higher than 80,i did a facotory reset reinstalled all my apps found problem still there so starteded to check all my apps usages etc i began to delete suspect apps...