change fps but keep speed for gif export

Hello. I'm creating a couple gifs for my employer. One thing is of course filesize, so I'd like to try export the animation as a gif with fewer images but keep the overall duration.

Can I do that without having to move all keyframes manually? Like, if I want to have the same animation with half the number of frames, is there a better way but half the framerate and move each keyframe manually to a new position?

Thank you