Siez problem images too big

Hello everyone. Im having trouble resizing the image that it would be around 150k. The limit size option does not seem to work as it only pulls the image to around 500 kb and ofc the images are not large in dimensions 1000 on longer edge [that makes around 1000x600 nothing big]. Ive tried reducing the dimensions dpi to 100 still 500k in size. If I edit it in windows  after some simple modification it easily reaches 170k size after save. Something wrong but what?

What could be the problem? . Thanx...