Hi Fery. Great question. The Android Gradle plugin generates a dependent task for each compile-time dependency as seen here using task-tree plugin.

$ ./gradlew :app:testDebug :app:taskTree --no-repeat
------------------------------------------------------------
Project :app
------------------------------------------------------------
:app:testDebugUnitTest
+--- :app:assembleDebugUnitTest
|    +--- :app:compileDebugUnitTestSources
|    |    +--- :app:compileDebugUnitTestJavaWithJavac
|    |    |    +--- :app:compileDebugJavaWithJavac
|    |    |    |    +--- :app:generateDebugSources
|    |    |    |    |    +--- :app:compileDebugAidl
|    |    |    |    |    |    \--- :app:prepareDebugDependencies
|    |    |    |    |    |         +--- :app:checkDebugManifest
|    |    |    |    |    |         |    \--- :app:preDebugBuild
|    |    |    |    |    |         |         \--- :app:preBuild
|    |    |    |    |    |         +--- :app:preDebugBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportAnimatedVectorDrawable2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild
|    |    |    |    |    |         |         \--- :app:preBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportAppcompatV72600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportConstraintConstraintLayout102Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportDesign2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportRecyclerviewV72600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportCompat2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportCoreUi2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportCoreUtils2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportFragment2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportMediaCompat2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportV42600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         +--- :app:prepareComAndroidSupportSupportVectorDrawable2600Alpha1Library
|    |    |    |    |    |         |    +--- :app:preDebugBuild *
|    |    |    |    |    |         |    \--- :app:preReleaseBuild *
|    |    |    |    |    |         \--- :app:prepareComAndroidSupportTransition2600Alpha1Library
|    |    |    |    |    |              +--- :app:preDebugBuild *
|    |    |    |    |    |              \--- :app:preReleaseBuild *
|    |    |    |    |    +--- :app:compileDebugRenderscript
|    |    |    |    |    |    +--- :app:checkDebugManifest *
|    |    |    |    |    |    \--- :app:prepareDebugDependencies *
|    |    |    |    |    +--- :app:generateDebugBuildConfig
|    |    |    |    |    |    \--- :app:checkDebugManifest *
|    |    |    |    |    \--- :app:processDebugResources
|    |    |    |    |         +--- :app:mergeDebugResources
|    |    |    |    |         |    +--- :app:generateDebugResources
|    |    |    |    |         |    |    +--- :app:compileDebugRenderscript *
|    |    |    |    |         |    |    \--- :app:generateDebugResValues
|    |    |    |    |         |    \--- :app:prepareDebugDependencies *
|    |    |    |    |         \--- :app:processDebugManifest
|    |    |    |    |              \--- :app:prepareDebugDependencies *
|    |    |    |    +--- :app:incrementalDebugJavaCompilationSafeguard
|    |    |    |    +--- :app:javaPreCompileDebug
|    |    |    |    \--- :app:prepareDebugDependencies *
|    |    |    +--- :app:incrementalDebugUnitTestJavaCompilationSafeguard
|    |    |    +--- :app:javaPreCompileDebugUnitTest
|    |    |    \--- :app:prepareDebugUnitTestDependencies
|    |    |         \--- :app:preDebugUnitTestBuild
|    |    |              \--- :app:preBuild *
|    |    +--- :app:processDebugJavaRes
|    |    \--- :app:processDebugUnitTestJavaRes
|    \--- :app:mockableAndroidJar
\--- :app:compileDebugUnitTestJavaWithJavac *
(*) - subtree omitted (printed previously)

However profiling seems to suggest that each of the prepare* tasks take around 2ms each if the dependency is already cached so this should not impact your build too badly (unless you are unable to cache dependencies for some reason than this becomes a bigger problem).

$ ./gradlew --profile --offline testDebug

The biggest offenders here seems to be mergeDebugResources and processDebugResources so that may be where you want to focus your efforts.

Hope this helps!