We report on a detailed experimental study of capillary condensation-evaporation processes of N2 in ordered mesoporous SBA 15 silica. We have carried out measurements of boundary hysteresis loops, reversal curves and subloops in order to test whether this material behaves as an assembly of independent cylindrical pores open at both ends. With this data, we come to the conclusion that, whereas the boundary hysteresis loop has the classical shape of type H1 associated with condensation-evaporation in cylindrical pores open at both ends, the capillary evaporation does not take place at equilibrium as it is generally assumed. Moreover, the pores do not desorb independently of one another.