I found that my prototype with realtime API start work very slow (more than 200-500 milliseconds for collaborative map set operation and this number still grows after 10-20 changes.
You can try oficial Playground https://realtimeplayground.appspot.com with "Edit the demo Collaborative String"
After each changes in the String textarea rtpg.string.field.setText(newValue) starts to run slower and slower from 10 to 300 milliseconds (after 30-40 changes).
What is the performance of realtime API, how it can be increased?