I'm uploading texture sequence of 27 png images, 3.5 MiB. In Deep AR Studio it takes 12 MiB. Any suggestions how to optimise it?

why is the size increased almost 4 times in the studio? The resolution of the pictures is 512x512

You can send us the images to test, but typically here are some standard tips:
Only use PNG if you need transparency
Try reduscing the size to 256