Higher speeds and better latency in theory are unrelated. And in certain implementations higher speed actually means more latency. Think about how fast a plane with full load of people operates. The traffic control, security checks, etc. imposes all sort of costs in time so that you can fly from Los Angeles to San Jose for about the same amount of time as you can drive from L.A. to San Jose. And most of the time in that flight is lost to all the non-flying issues, i.e. more latency. Whereas driving, you hop in your car, may lose a little time for fueling up, and you are good to go so very low latency. And it is obvious cars are much slower than planes, but it is much lower latency for short distances.
Networks will do similar things, in order to maximize the utilization on a fiber, they will aggregate data, and then send them at high speeds, but this adds latency to your packets. Of course if you are willing to pay more to get dedicated fiber, path, then you can have both higher speeds and lower latency, but you can bet most service providers are not going to give that away for free.