These can be some of the factors for slow scrolling in your code :
setImageResource() does Bitmap reading and decoding on the UI thread, which can cause a latency hiccup. If that's a concern, consider using setImageDrawable(android.graphics.drawable.Drawable) or setImageBitmap(android.graphics.Bitmap) and BitmapFactory instead.
Size and resolution of your images can also be a cause of slow scrolling, try creating thumbnails images of your large images and use.
try to using pagination instead of loading complete data.