Some other common things to optimize are:
- Texture usage (try and make textures smaller and re-use as many as possible - things like Normal Maps etc can be smaller than Diffuse maps - experiment)
- Make sure “Tick” is turned off on as many actors as possible
- Make as many materials fully “rough” as possible (no reflections)
- Remove Transparency from materials where you can (like OORTIZ says)
- Any areas that are slow, try and box them in so that they don’t have a large draw distance
- If it’s still slow - you may need to look into reducing the landscape resolution