Uhh.. did someone remember my map? (I just posted it 2 days ago so...)
I have a huge problem, i almost finish it (for alpha) and mirrored it... but when i mirrored it, the time for the compile lasts forever...
And i don't know how to optimize!
Step one, learn how to use func_detail properly. Basically, anything that's not a large wall or floor or ceiling should probably be converted to func_detail to tell the compiler to ignore it when calculating what players can see from where — for example, steps in staircases, sloped roofs, any sort of trim, small shacks... as an extreme example, all three of the control point buildings in Gravel Pit are func_detail because the walls are full of big gaps that prevent them from fully blocking the view of anything significant.
That said, if this is your very first version and you're already needing to make judicious use of func_detail, you probably introduced too much detail for an alpha.
Alternatively, you might have introduced errors in the compile. A leak — which is very possible if you mirrored your map, like say you forgot to select one critical brush before you copypasted — will wreck your compile time in addition to the map itself. Try running just VBSP and see if there are any issues reported.