Camper shells for the Ford F150 are generally designed to fit specific model year ranges, so a camper shell intended for an early-1990s F150 is unlikely to fit a 2015 F150 correctly. In addition, camper shells are intended for specific cab and bed combinations.
The Ford F150 truck has gone through several design iterations over the past several years, with major model refreshes in 1997, 2004 and 2009. Camper shells often fit F150 trucks produced in the years between model refreshes, such as all 1997-2003 models. However, camper shells are not always compatible between trucks with different cab and bed layouts, even within the same model year range.