Revealing mistake: During the scene where Lara and Reiss's henchmen are fighting in the lab with the orb, look closely: the computer monitors in the background briefly flicker (as most monitors appear on camera), indicating they were shot in the background. During the close-ups, this does not occur.
Revealing mistake: When Lara and the guy race with their bikes by the Great Wall, Lara's stunt is noticeable because her face is rounder and not so angular.
Answer: The pressure in the temple would be the same as that of the water just before Lara entered the temple. So no she would not need to decompress before entering at the temple as it was open to the sea, but she would have surely suffered the bends on the rapid accent to the surface.