Yes, you will need support material. Pretty much... any angle more than 45 degrees is difficult to print without support material. The good news is, because the support material is on the back side, nobody will see the marks when you peel it off of the buckle. I would probably use rectilinear support on this.

Also, you can generate the object with support built in as part of the design. I would be tempted to do this on the buckle.