Latency issue in BLE LLPM


I am trying the BLE llpm code and made some changes in the existing sample code in the data length to 8 bytes from 4 bytes. 

When transmitting a data of 8 bytes, I am receiving a latency response around 10ms. Does this llpm code works in 1ms for smaller data length or should it work for any data length (max 20 bytes)

Thanks in advance