Cannot import Android class R with Fabric and API15

[bjameswebilize]

I’m trying to integrate the Fabric SDK into my Android project (API 15) running on Android Studio.
After included all appropriate entries into both build.gradle files, I end up with a successful build, but my code now doesn’t recognize the Android R class.
It gives me “Cannot resolve symbol ‘R’” in my imports with a big red in letter R:

import com.example.myapp.R;

Here is my project build.gradle file:

apply plugin: 'com.android.application’
apply plugin: ‘io.fabric’

android {
compileSdkVersion 15
buildToolsVersion “23.0.2”

defaultConfig {
    applicationId "com.example.myapp"
    minSdkVersion 15
    targetSdkVersion 15
}

buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.txt'
    }
}
compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_7
    targetCompatibility JavaVersion.VERSION_1_7
}

}

dependencies {
compile 'com.android.support:support-v4:18.0.0’
compile 'com.facebook.android:facebook-android-sdk:4.7.0’
compile(‘com.twitter.sdk.android:twitter:1.10.0@aar’) {
transitive = true;
}
}

And here is my Top level build.gradle file:

// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
repositories {
jcenter()
maven { url ‘https://maven.fabric.io/public’ }
}
dependencies {
classpath 'com.android.tools.build:gradle:1.3.1’
classpath ‘io.fabric.tools:gradle:1.+’
}
}

allprojects {
repositories {
jcenter()
// To Facebook SDK
mavenCentral()
// To Fabric SDK (Twitter)
maven { url ‘https://maven.fabric.io/public’ }
}
}

The problem solves if I comment the dependency in my project buil.gradle below

    compile('com.twitter.sdk.android:twitter:1.10.0@aar') {
        transitive = true;
    }

or if I upgrade to Android API 23

Unfortunately I’m working with a wearable equipment that only supports API 15 and since Fabric is compatible with it, there should be a solution for this.
Any suggestions?

Thanks in advance.

[niall]