Does deleting call history improve memory use?

Per-call history is going to take a handful of bytes at most. You'd have to delete a huge list of previous calls to make any significant impact to memory usage.

What is it you're trying to achieve here?

No. The storage space that the calling list occupies is so small that it is negligible. Note that most amount of storage space is occupied by media data/files. Deleting Photos, Videos, Music etc will generate the most space in a short time.

Axel F.