By saying stock truck, they are referring to your lift pump. You have probably seen the FP psi's posted by the members that are using the pusher pump system, most are well above 15 @ idle. If you go the route of an aftermarket, single lift pump, you could also go way over 15 psi's @ idle if you do not regulate the psi's down via the dead head on the pump, if it has one, or a external regulator (can be either dead head, non returning or a return/bypass type of regulator, that returns the unused fuel back to the tank by using a seperate fuel line as a return). Some of the high flow lift pumps are not dead head regulated and require a seperate return to adjust psi's, which can go as high as 45 psi's at idle, way too much for our application, the psi's, that is. Sooooo,, unless you plan on adding a non-regulated and high psi aftermarket pump ( the Mallory 4150, for example, can only see about 14-15 psi's max at idle, there are others, such as the $99. 00 Summit pump, which state that they put out about 18 psi's at idle) a 15 psi FP gauge should be fine, especially if you mount the sender in a post filter location, as there is some loss of psi's through the fuel filter.
Scott W.