If your CAS latency is higher than what is advertised (e.g. latency is advertised as 3000c15-18-18 but runs at 3000c16-18-18), this is because of a BIOS setting that helps with memory stability on Ryzen systems.
You can disable this setting so that the memory runs at its rated speed. However, depending on the quality of the memory controller in your CPU and motherboard, doing so may result in your memory not being stable.
Depending on what motherboard you have, the method for disabling the setting will differ. If you are unsure of how to disable the setting, please consult your motherboard's manual to find the appropriate setting. For reference, the screenshot below shows how to disable the setting, titled "Gear Down Mode," on ASUS boards.