Mac wakes up from sleep every night and then goes back to sleep immediately
I'd eliminate any external devices as the cause of waking first. You can set the MacMini to go to sleep automatically, then eject/unplug all external devices.  KVM &amp; Mice are the usual suspects...  


  (Port 1 of Hub at 0x15000000) may have caused a wake by issuing a
  remote wakeup (1)


If you haven't already, you may be able to identify the USB device suspected of issuing the remote WakeUp call. 

About this Mac > System Report > Hardware > USB > USB Device Tree 

or use the shell command system_profiler SPUSBDataType