Hey Den75,
I just had a quick run around on your map and I like what you've done!
I have a few small suggestions to improve the map performance because I drop from 80+ fps to 40+ in places.
The first thing you need to do is reduce the undergrowth density from 10 to like .5 on two of your materials. That is causing the major issue. The second would be too reduce the draw distance from 100 to 75-80 meters. It's a dark map and to be honest I really don't see an advantage.
Tweak those settings and test it locally in the single player mode. I bet you'll see a huge performance boost.