There are three files which contain linked images in your downloaded folder. Choose one of them. Either the:
Start by tracing the object. Avoid making the mesh in one large shape. Trace the image strategically, so you can create the meshes on each object rather than the whole images. If you wish, you can copy the placed photo to the second artboard to trace on top of it.
The goal with the gradient mesh is to be as photo-realistic as possible. You don’t need to replicate each detail of the photo’s gradients. The point is to use the photo as inspiration to create a photo-realistic object.