Penalty rules question

[Chandemonium]

On the play where decker got called for taunting and there was also holding on the o-line, why was it first and 20 after? Shouldn't the 15 yarder have superseded the 10 yarder to make 1st and 25?

[mannc]

On the play where decker got called for taunting and there was also holding on the o-line, why was it first and 20 after? Shouldn't the 15 yarder have superseded the 10 yarder to make 1st and 25?

or tacked on, since it was a dead ball foul?