Moving keyframes with duration change
Since this is a still image, what you can do is use the "Rate Stretch" tool (keyboard shortcut: R) and stretch the image shorter. If the keyframes don't move with the Rate Stretch tool, you can always create a "Nested Sequence" of just the image (Premiere Pro's rough equivalent to an After Effects precomp) and then rate stretch your nested sequence. This will stretch both the image and the keyframes together.