i get that but it suddenly went from around 30 minutes to 4 hours with only small changes. is there really nothing wrong?

so i am building a custom zombies map and i am pretty much done. the problem i have is everytime i try to compile it litterally takes hours. there are no major errors so i really don't know what's going on.
my processor is running at 40% and the mod tools are using around 1.5GB of ram...