They might since they bolt onto the lug nuts and don't clip to the outer rim of the steel wheel like most wheel covers. Do you have the 16" wheel covers and lug nuts? I would just take one along and see if they fit on the steel 15 " wheels without hitting the edge of the rims. I see you are talking about ordering some. Maybe check on some 15" wheels at a salvage yard just to see if they fit?
Thomas
the "Mustang Guy"
1987 5.0 LX Mustang
2016 Mustang GT - current daily
2004 Satellite Vibe &
2009 Red Vibe GT -twin's cars
2003 Neptune Vibe GT - prior daily
2010 Red Vibe GT - RIP 6/16/14
2006 Platinum Vibe - son's car