Proton decay modes in SU(15) grand unification

In the SU(15) grand unification model, proton decay is mediated by Higgs bosons only. They can be $B+L$ or $B-L$ conserving, depending on the choice of the Higgs sector. The dominant decay modes involve different generations of fermions. Thus, kaonic final states are preferred over pionic ones. If some discrete symmetry is imposed on the model, the proton can even be absolutely stable, unlike the situation in any other grand unified model.