3000mhz CL15 has a true latency of 10nS. 3600mhz CL19 has a true latency of 10.5nS. The 3000mhz CL15 kit would be faster, however, the timings on a CL15 kit are not going to be conducive to good compatibility with Ryzen platforms. You would be a lot better off to find a set of high end sticks from G.Skill, or whoever you prefer if you don't like G.Skill which it seems maybe you don't, that are either CL14 3200mhz or CL16 3600mhz, because the 3200mhz CL14 sticks would assuredly be compatible with your Ryzen platform for 99% of 3200mhz CL14 kits, since those are going to be Samsung B-die chips and would have an 8.75nS true latency, or a 3600mhz CL16 that would be only marginally slower at 8.8nS true latency.
"Speed/frequency", contrary to what a lot of people will tell you, does not "trump" true latency. True latency IS the measuring stick for how fast memory operations will generally be based on a COMBINATION of speed and CS latency. So sticks with a lower true latency are going to be faster, period. 4000mhz sticks with a CL22 latency are not going to be "faster" than 3200mhz CL14 sticks because the 4000mhz sticks are going to have a true latency of about 11nS.
ALSO, on Ryzen platforms, so far at least, once you go beyond 3600mhz you are almost certainly (To the point of being guaranteed for most configurations, although some systems with a very good CPU sample, high end motherboard and superior memory modules might be able to go as high as 3733 and in very rare cases possibly even 3800mhz although I haven't seen anybody actually accomplish this and show proof of it. It's been entirely anecdotal from what I've seen.) going to lose the benefit of a 1:1 ratio state for the infinity fabric as for MOST configurations, going beyond 3600mhz and certainly for the vast majority of users, anything over 3733mhz is going to incur a 1:2 ratio penalty. That is going to SIGNIFICANTLY increase the latency along the lines of 5-9nS in most cases depending on what the actual frequency is set to for the memory.
If you buy a very high end 2 x8GB 3733mhz CL16 kit, you'd end up with an 8.57nS true latency which, short of trying to further tighten those timings down, which might be possible, you'd end up with about the fastest memory configuration you could legitimately have without incurring the ratio penalty from the infinity fabric, IF you can get them to run at 3733mhz without decoupling.