Available up to 52 and in regular as well as wide are the Shimano 80 series shoes (both road and mtb) and Sidi Genius (road) and Dominator (mtb). I have a solid 15+/16 US foot. No way I could fit into a Nike 15. New Balance 15W or EE fit "ok" (just). 16's tend to run a touch long for me and the choices really go down.

I have standard width Shimano and Sidi 51s. I've not tried the Shimano wide version. But, the Sidi "Mega" (their wide) is extremely voluminous and seems to not have much wider a foot bed or toe box.

Hope this helps some.