The Precision 7530 is a powerful and hefty workstation, but it's definitely not smaller than the XPS 15. Dell has confirmed a minor measurement error on its product page and will update the dimension from 337.6 mm to a more accurate 375.92 mm.
https://www.notebookcheck.net/Dell-accidentally-lists-laptop-over-an-inch-smaller-promises-to-fix-the-error-soon.354866.0.html