Hi Photoshoprint,
I'm stuck with a laptop because I travel from country to country and have no permanent residences where I can safely store desktop systems.
I actually finished the image in Photoshop CC because for some reason it performed better than the 2014 version, it still created huge temp files and had the same problem with the preview image, but I managed to finish the panorama without running out of disk space (200Gb+), with 6 history states enabled, whereas 2014 just ran out of space with only 2 history states.
I originally used the auto panorama feature for all the photos, but that produced a fruit bowl type panorama by severely distorting the images as they approach the outer edges and curving them upwards.
Instead I worked with four images on one row at a time, then merged them and locked them as a single layer before adding more and repeating the process for the entire 6 rows. That still produced a slightly curved final image (no doubt due to lens distortion that the stand-alone 'DxO Optics Pro' couldn't correct), but at least everything was in the right place.
It took a long time to do, because every action generated vast temp files and I had to save it after every stage under different file names because of the limited history.
There are programs out there with unlimited undo that don't create vast temp files and I remember using Picture Publisher for many years with that same feature, even several thousand undo's on one occasion.