This is the same as "You built it in InDesign; now I need it in Word so I can edit it myself and cut you out of the process."
The two programs are not compatible in that sense. They don't do the same thing and they're not built for the same task. Copy and paste as many elements as you can, but resign yourself to re-creating everything in Keynote.
And bill the bejabbers out of your client for it. If you/the client inherited the job, it's no one's fault, but if the job was originally specced in InDesign and someone knew it would need to be editable in Keynote, that's on the person who did it in ID first. The only "speed" here will be how fast and how good you are in both programs.
Not the same topic, but related answer here:
What can a designer do if a client claims that the work delivered is unacceptable and refuses to pay?