Hello Fossil,
The fan configuration that comes in the HL15 does not support any sort of RPM control in it’s default config. This was something that I brought in a recent post I make talking about my first impressions on the HL15.
If you look here, you can see that the fan connectors are all wired directly into the custom 20-pin connector that powers the drive backplane. You CAN unplug all the 2-pin adapters from the fan 3-pin holder and use the headers on the motherboard. However, I don’t think I have ran into too many motherboards that have 6 3/4-pin fan connectors. I suppose we could just use a few splitters. Or maybe something like this would be ideal to use.
I strongly dislike the fact that the 2-pin fan adapter does not unplug from the power PCB breakout. I do plan on adding my own fan hub to have some control over the fans as I also purchased the Chassis as a bare-bones system. Keep in mind that if you plan on doing this you will want to strongly consider running an actively cooled CPU cooler.