you cannot fit all your images on the gpu at once.
you cannot directly upload png to the gpu without decoding.
so depending where you’re bottleneck is - which bjoern described how to find it out - you’ll either have to go for a less cpu intensive imagecompression or if reading is the trouble you need a faster ssd/raid.
another thing to try is adjusting Threads IO, Threads Texture and IO Buffer Size but since you’re already down to 9 fps i’d not expect to much of these tweaks