Your device should be running at least OS X 10.14 (Mojave) to use URC TV smoothly, and you should also keep your web browser (ideally Google Chrome) updated to the latest available version. At least 1GB of RAM is required, though preferably more as RAM is a shared resource across all applications on your computer. Closing down additional applications and minimising the use of browser plugins will all help if your device is low on RAM, as will a restart if your computer has been running without a shutdown for a long time. Your internet connection must also be sufficiently strong.
If you are using Airplay to cast to Apple TV, make sure you upgrade to tvOS 16 for the best experience.
You can learn how to test your internet speed here.