Entering keystrokes with the Apple TV remote is not fun. IT suggests downloading the free Remote App so you do not have to arrow from character to character. The Remote app for iOS will display a keyboard on your iOS device that you can type on. It's worth the time it takes to download the app and pair it with your Apple TV for those inevitable times you'll need to type a passcode, account credentials or custom messages.
The Remote app uses Home Sharing, which needs to be set up on the Apple TV and on the device on which you will use the Remote app. On Apple TV, this involves going to Settings>General>Remotes>Remote App.