Anyway you can see that Map Generator is generating a map at the bottom of the Java client, so there is no advantage as you can cancel match in lobby.
Matchmaker Rotation/System Comments
If somebody has problems with the map "Mavys Marsh" let me know, I had reports of people getting low fps on it but I don't really have any problem on it. I don't know how large of an issue it is.
Long story short: yes, there is a glaring, technical issue with the decals that are causing this performance issue. It can easily be fixed as I will outline, but it should be removed from the pool and labeled with performance issues until addressed.
I am not at my PC right now, but will show why this is happening later by looking at the map draw distances for decals in the editing tool.
Mavvy's marsh has EVERY decal at a maximum, allowable draw distance (5000 or greater game units of height) while most maps are about 300-500 (basically "zoomed-out" view while in game). The engine has a hard time processing all of this information and is not meant to be pushed to this limit.
I recommend removing it and sending a note to Chosen to fix it, be given a chance to address the issue (finally).
There are methods for "macro" decals where you can have certain, enlarged decals drawn while zoomed out, but not in. I recommend he does this if he is unhappy with the visual degradation.
Holy mother... okay it is worse than I thought:
So he has THIRTEEN THOUSAND DECALS which is like 40x more than any i have seen on any map. this guy must have spent a month just placing them??
For reference, I checked some 20x20s such as "Selkie's Isle" which has ~3600 decals. Mavvys Marsh is 10x10....
This map is just way way too detailed for the FAF engine.
Chosen without a doubt needs to fix this and tone down the decal count and draw distance issue.