DIAGNOSIS The internal storage is likely near capacity from cached app data, causing system slowdown. The Google TV interface requires free space to operate smoothly.
FIX First, clear the cache. Go to Settings > Apps > See all apps. Scroll to and select Google TV. Select Clear cache. Do the same for the Google Play Store app. Next, manage storage. Go to Settings > Device Preferences > Storage. Select Internal shared storage. Review and delete any unnecessary app data or cached files. Ensure at least 1GB of space is free.
IF THAT DIDN'T WORK A background process or automatic app update may be causing the lag. Perform a soft reset. Hold the physical power button on the side or back of the TV for about 10 seconds until the unit powers off and restarts itself. This clears active memory without affecting settings.
HEADS UP Do not perform a factory reset as a first step. If you must, know that it will log you out of all apps and erase all picture calibration settings. You will need to re-enter all login credentials and re-run the Acoustic Auto Calibration if you used it.