Is the performance gain of short unreadable json keys worth the data size difference?

One of the lead engineers at my company is convinced that the data size difference saved by using 1-2 character json keys is significant after accounting for large scale ~500million requests per day. I strongly believe that it’s not, and that making them human readable is more important but don’t have the data to back up my claim.
Unfortunately I feel like it would take me several days of effort to parse our json and calculate the true answer. Is there some outside evidence I could point to back up my claim. Is he actually correct?