I'm gonna go against the grain here and say (and, you can trust that the advise will work as I'm not one of the hundreds of drummers on the internet asking the same question.) Haha.
When approaching anything speed related, playing "slow" will never help your body understand what you're asking of it.
Another point is that as you increase in speed....multiple muscle groups are used but, not all of them are used at the same time for those different speeds.
In other words...playing 16ths at 100bpm will never help you get to 200bpm.
Yes, it will help understand the space issues (which are more important in the long run) of the notes and yes, you absolutely need to play slower to gather this understanding but, that has nothing to do with asking your leg to make fast repetitive motions....only playing fast repetitive motions do that.
So my solution has always been to start your tempo at the fastest point your weakest limb can play.
So, if your right foot is able to stay in time at 160 and your left cannot....well, start at the point where your left can start and work from there.
Now, after you run that for 30 minutes a day
Then start working on stick control with your feet.
The key to building speed is to do both!!!! You have to play slow to understand the space but, you also have to play fast so you body understands what you're trying to ask it to do.
Nothing wrong with the "playing slow" advise....you need to do that but, I think a lot of drummers automatically throw that out there simply because that's what everyones saids....not because it works.
I mean think about it....would the internet be full of the same questions from drummers all over the world if playing slow was the gateway to playing fast? I don't think so.
Do both, play slow AND play fast.
Cheers,
D