Inaccurate info from Ford. The regular 3.5 ecoboost in the F-150 is boosted to 16psi. The Raptor is 18psi, published in many auto journalism sources.
First, the K04 turbo it uses would be totally wrong for an OEM application that only wanted 13psi. They simply would have used a different turbo housing.
Second, you really think there is something so magical about the Raptor 3.5 that allows it to produce way more power and torque than the regular 3.5 truck engine while boosting less?
There is some headroom in the stock turbo setup, enough to boost to 21-23 psi peak but no more than that given the limitations of the KO4. The real questions are going to be if the 10-speed gearbox can hold the torque and if the stock fueling can support that boost level.