I don't see the need for an XL version just to fit a D15 cooler.
The D12L comes so close to the D15 in reviews that it's just not worth it. (Example: https://www.guru3d.com/articles_pages/noctua_nh_d12l_cpu_cooler_review,8.html )
The D15 would only really fill a very narrow gap between the...