No it's not going to hold the weight over time. Looks like that box is on joist. You can use if IF you run proper size screws for fan weight thru the mounting plate, thru box and into wood, so that the mounting plate is fastened to wood.

They have boxes for ceiling fans that are shaped to go over joist, but it will be centered on the joist and I cannot tell from picture if that what you have. If it is you can just replace the box.