I recently upgraded my Macbook Pro to the latest version (Mid 2015) with the Nvidia graphic, 16gb ram and 512gb ssd.
I have now experienced that while using PS, mail, safari, spotify etc it has a tempeture of roughly 41-45 degress. But as soon as I open LR....it goes up to 85-90 degrees :-/
It's only LR that is having this effect on my Macbok Pro. I have deactivated the GPU, Face recognition etc tec but it doesnt Work
Please open Activity Monitor on your machine and check which processes consuming maximum memory, try end those and run Lightroom only at a time.
Have you had any heating issue on you Macbook Pro in the past.