Gradle builds really slow with a multi-project structure

Question

When building with gradle on a multi-project setup containing roughly 140 projects/libraries, the build time took 1 hour and 22 minutes. And i was using --parallel

Answer 1

Doing a clean you actually delete the already predexed libraries.
As suggested in this thread you could save some time on clean builds by disabling predexing (because at the next build they will be deleted):

android {
  dexOptions {
    preDexLibraries = false
  }
}