Very Poor compression

I started using this plugin today and I tested it on a 1.6M image ( https://goo.gl/C9WdNp ). After uploading to my wordpress site it has 1.4M ( https://goo.gl/3P60Ol ). When using Photoshop in the same 1.6M image to save for web with a high quality (60), it has only 378Kb. So I am a little frustrated because I was expecting more. Besides this I can’t understand why uploading one image uses 12 credits.