Resources.LoadAsync and AssetBundle.LoadAssetAsync make lags in main thread

Resources.LoadAsync and AssetBundle.LoadAssetAsync in unity 5 makes a lag on Android. For example I asynchronously load image 1024*512 and profiling frame durations. In general durations are beetween 10 - 30 milliseconds, but always there are one big frame duration in 100 - 300 milliseconds. As bigger image, as bigger this one duration. As I understand asynchronously process, it should't affect main thread. Any ideas to avoid this lags?