编辑build.gradle无法解决minSdk（API，N预览）！= deviceSdk（API 21）

Question

当我将compileSdkVersion从'android-N'和targetSdkVersion从'N'更改为build.gradle minSdk中的整数21（API，N预览）！= deviceSdk（API 21）未解决。任何提示？

apply plugin: 'com.android.application'

apply plugin: 'com.android.application'

android {
    compileSdkVersion 21
    buildToolsVersion "23.0.3"

    defaultConfig {
        applicationId "com.noureddine_ouertani.www.wocelli40"
        minSdkVersion 15
        targetSdkVersion 21
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:24.0.0-beta1'
}