Between the time I posted & then got your response I uninstalled and removed all database files from the server, then uploaded & created a new install & db tables. I then tried to add images during the install. It froze at 135 of 155, but only recognizes 81. link is: index.php?gallery=1&theme=dark.
I then did as you requested and uploaded a test folder with 9 images. It processed all 9 within 15 seconds and shows 9 in the gallery. One of the pictures is 1.33MB.
The original pictures are all from the same batch and none are over 713kb. Average dimensions of each pic is 3000x2000. Hope this helps...