AssetBundle.LoadAssetAsync is about 4 times slower on android than on ios devices

Hi, All! It's incredible! Anyone can help me out?

The test results for the same assetBundle: result: iphone6 5 seconds iphoneSE 5 seconds ipad Air2 5 seconds Galaxy Note7 20 seconds (Android 6.0.1,Snapdragon 820,4GB RAM)

unity version: 5.4.0f3 AssetBundle size: 17.3mb.

Below is the code of loadAsset.

 WWW www = WWW.LoadFromCacheOrDownload(url,version);
 yield return www;
 if (www.isDone)
 {
 bundle = www.assetBundle;
 NGUIDebug.Log("WWWFinishTime:"+Time.time);
 AssetBundleRequest request = bundle.LoadAssetAsync(name, typeof(GameObject));
 yield return request;
 NGUIDebug.Log("ABLoadFinishTime:" + Time.time);
 GameObject obj= Instantiate(request.asset as GameObject);
 }

And the create assetBundle code:

 [MenuItem("AssetBundle/Build AssetBundles -IOS")]
 static void BuildAllAssetBundlesIOS()
 {
 BuildPipeline.BuildAssetBundles("Assets/AssetBundles/ios", BuildAssetBundleOptions.None, BuildTarget.iOS);
 }
 
 [MenuItem("AssetBundle/Build AssetBundles -Android")]
 static void BuildAllAssetBundlesAndroid()
 {
 BuildPipeline.BuildAssetBundles("Assets/AssetBundles/android", BuildAssetBundleOptions.None, BuildTarget.Android);
 }