It sounds like you're experiencing severe lag (especially if the game is freezing one you like that).
Here are some ways to reduce lag:
- Turn off water reflection (Options/Esc>>Video>>Uncheck Water Reflection)
- Turn down View Distance (Options>>Video>>Turn down View Distance)
- Remove any unneeded maps from your Exports folder
- If the lag gets too bad, you can give your computer a short break by turning your camera toward the sky, where the game has less to render on the screen.
- If lag continues, and you have any extra maps (other than Water Mill) in your FH>>Media>>Terrains folder, try removing these maps by removing their folders from your Terrains folder. These will remove them from Map Maker, but if you can always put them back into Terrains if you want to continue working on them at a later time.