assetBundle.LoadAssetAsync performance on android and ios devices

hey,guys.I face a problem that assetBundle.LoadAssetAsync take different time on android and ios device.
I use assetBundle.LoadAssetAsync just like this

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);
}

AssetBundle Build like this

  [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);
        }

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

Someone help me?THX.

Here is my package
79723-ab.png
Asset name is just same as the bundle name