15's are rare Bruce, and becoming even more so now that Escape has suspended production of them. It's still the best use of space in any Escape model IMHO, and highly desired.
17's do come up for sale here quite often, partly due to what we call "two-foot-itis" (the tendency of some 17 owners wanting to upsize to a 19, or 19 owners wanting to upsize to a 21, etc). You also have the option of a new build, which you can truly customize to suit your needs.
Best of luck on your search, and welcome!
"You can't buy happiness, but you can buy an RV. And that is pretty close."