I can't dl or view it right now but I can still guess. ( ^ ninja guessed

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First, check for leaks. You probably have some really large areas that leave tons of open space in an outdoor map. If there are unused areas inside the gameplay world you need to fix them. Fill them with solid, put them in the skybox or do a better job sealing areas off.
Even outdoor areas follow the same principles as indoor areas. You need to limit sight lines and playable areas. Sightlines is the most important.
My guess is there is a leak into a 'basement' of your map. By basement I mean a hollow unused space under you map. Say you put one huge sky 'box' around your level. That's bad.
It doesn't leak to void so it's not an error, but all that extra space still needs to compile for no reason.
Think of the outside as hallways and rooms that have a roof , just that the roof is painted sky. Bring that sky in as close to the play area as possible.
Like a canyon is just a large hallway, but halway up the walls and the ceiling have sky tex. That'll keep it optimized while giving the illusion its wide open, it will also let people jump high without hitting their heads.
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Something to try.
when compiling set options to
bsp - normal
vis -fast
vrad (lighting)- none.
run game -
unchecked
Any map with those settings that is sealed correctly should compile in a matter of minutes. 10 tops probably.
If it's going after 15 minutes it's time to seal it in better as I explained.
As UKCS said, lighting times are long, so doing a quick compile like I said will drastically reduce wasted time trying to find the problem. When all problems are solved do a non-hdr lighting and go ingame.
don't even waste time with hdr until you are getting close to finished.