The May 2012 Tip explained the meaning of a three segment composite position tolerance. A composite tolerance has one geometric characteristic symbol but multiple segments. This drawing is from that Tip. Datum features referenced in the upper segment of a composite tolerance are there to control the location of the pattern of features. If datum feature references are repeated in lower segments, they are there to refine the orientation of the pattern relative to the datum(s) established by the referenced datum features.
A possible gage that could be used to inspect the second segment of this composite position tolerance is shown here. The size of the pin in the gage would be equal to the smallest hole minus the position tolerance of 0.25. Or Ø14.95-0.25=Ø14.7 mm. This gage pin must be allowed to float while remaining parallel to the datum plane established by datum feature A. The gage calculation does not provide for gage tolerance or wear allowance. Since datum feature B is not referenced in the second segment, the gage would not close in tightly on datum feature B. This gage is only verifying the second segment of the composite position tolerance.