I did not understand what the importance of Shangri-La was then after lokking around i found something interesting the mines around the temple are filled with 115 if you cant find it just look around theres blocks of it everywhere
So i started to think about what this meant and how it links to the story i came up with 2 possibilities
1) The nazis found it and used it as a supply of 115 which explains the mine an how richtofen knows so much about it
OR
2) The 115 is what allows the temple to be used as a teleporter which explains how the crew arrived at the temple and how they time travel when you activate the eclipse as we know that 115 powers the teleporters so maybe it powers the temple in the same way
please leave thoughts and other theories as this is not complete but from what i could see noone had really looked into it on this forum (if they have i couldnt find it)