On our machine based on two processors Intel Xeon E5 calculation It took 90-100 minutes. These processors for servers that need a special motherboard, in our case it is the Asus Z9PE-D8 WS. immediately I warn that you can not put the two processors like i7 or i5, it supports only certain types of processors.
The causes of the long lighting build time may be a few, at the beginning lighting build time of our project take more than 2 hours. After changing the “lightmap resolution” settings for each of the models, the time required for lighting build was reduced. We used such lightmap resolution 32,64,128,256,512. Most models have a resolution 64 and 128. The walls and floors have 512. 32 and 64 were used for small objects such as cups, plates and books.
P.S. I always wondered how effective it would be to use Intel Xeon Phi for rendering and in this case, to lighting build. Unfortunately, access to the test platform is not easy… Maybe in the future lighting build will use GPU, it would be speeding up! 