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
Did you try setting the parameters of the Gradles compiler?
If you have remote dependencies, each time you run the project it will be operated with remote resources using the network. You should define the instruction to the Gradles compiler to that him to work offline using:
--offline
Here I leave you a screenshot of the compiler settings for better performance:
Or what is the same...
Source: http://gradle.org/docs/current/userguide/gradle_command_line.html