Why do my results of API testing on a VM improve with the quantity of tests

I'm currently testing my VM hosted on Google Cloud with the Postman API testing tool. My test criteria is that the response time is less than 50ms and that the status code is 200.

I've noticed that my tests usually start with errors and then improve as I rerun the test.

Why would this be, this the VM caching something to increase speed? The only test condition that fails is the less than 50ms test condition.

I attached the three tests conducted for a VM with 1 vCPU, 3.75 GB memory: Test 1, Test 2, Test 3 The improvement is clearly visible, and this pattern is common across 2vCPUs, 4vCPUs, and 8vCPUs

Any help with understanding this would be much appreciated!