In the 13 eV EI mass spectrum the intensities are:
Since the natural abundance of 13C is 1.1%. To a first approximation the intensity of the M+1 peak is 1.1% per C in the molecule. This would give 13.3 C's in the molecule. Rounded to 13. Alternatively, we can use table 2.2 in McLafferty, which lists the relative abundance of isotopic peaks for carbon. With C13 the abundance would be 14.3%. With C14 it would be 15.4%. This is consitant with the compound containing 13 C's. However, this is obviously not consistent with a molecular ion at m/z 154. This piece of information is not consistant.