Have you used the debloat tool?
New Fire TV Debloater Toolbox Now In TROYPOINT App.
Also have you turned off some of the Amazon garbage?
settings>preferences>privacy settings>Device usage data set to “off”>Collect App Usage Data set to off>Interest- based Ads set to off back out to the sub menu and select “Feature Content” > Allow Video Autoplay set to off>Allow Audio Autoplay set to off. Back out of autoplay and choose Sync Recent Content and click to turn off unless you use Amazon Prime. Now go to Display & Sounds >Screensaver and set the start time to “Never”.
These are small tweaks that help save space and cpu/gpu cycles thus speeding up your sticks response and allowing more free RAM.