Zephyr API Bulk Upserts

Currently, I'm working on improving the Performance of a program that among other things uses the Zephyr REST API to get and update Testcases.

This program in total does hundreds of API calls to Zephyr which obviously takes some time.

A simple test program (screenshot in attachment) shows that the execution time of REST calls is very unstable and sometimes even take multiple seconds just to get 10 Testcases.

My question is if there is any faster way to do this since there are no Bulk inserts/updates possible or at least I can't find them in the API documentation (https://support.smartbear.com/zephyr-scale-cloud/api-docs/#tag/Test-Cases/operation/updateTestCase).