Premiere Pro going slow -cannot save work

I hope that an experienced member can give me some help:
Using MacBook Pro, 16Gb RAM, 500Gb SSD, 2Tb external drive, I have been happily editing 9 sequences of our East African safari trip and I am 95% done with the project.
Since a few days while adding last touches, I suddenly got error message: :Your Mac OSX startup disk has no more space available for application memory".
I have checked every thing I could think of: when the project and all the clips are loaded and ready for me to process in Premiere Pro, I am left with 84Gb free on my SSD and 418Gb free on my external drive. My preferences are set so that Premiere can use 13Gb RAM and other applications 3Gb.
To give you an idea of the extend of the 9 video sequences: each is between 36min and 57min long, when starting up Premiere is loading just under 3000 videoclip all in HD 1920×1080.
I am exporting the sequences as 1280 x 720.

I am now stuck as every smallest change I am making is taking ages for the program to respond and when trying to save the save window shows the yellow bar to reach 50% and then gets stuck – I can not save and have to terminate Premiere Pro.
Have I reached the limit of Premiere’s capability or what could be the cause?

via Video Editing Forums: Digital Director – Adobe Premiere, Premiere Elements, and After Effects