If a person indicted for murder be found by the jury guilty thereof, they shall in their verdict find whether he or she is guilty of murder of the first degree or second degree. If the person indicted for murder is found by the jury guilty thereof, and if the jury find in their verdict that he or she is guilty of murder of the first degree, or if a person indicted for murder pleads guilty of murder of the first degree, he or she shall be punished by imprisonment in the penitentiary for life, and he or she, notwithstanding the provisions of article twelve, chapter sixty-two of this code, shall not be eligible for parole: Provided, That the jury may, in their discretion, recommend mercy, and if such recommendation is added to their verdict, such person shall be eligible for parole in accordance with the provisions of said article twelve, except that, notwithstanding any other provision of this code to the contrary, such person shall not be eligible for parole until he or she has served fifteen years: Provided, however, That if the accused pleads guilty of murder of the first degree, the court may, in its discretion, provide that such person shall be eligible for parole in accordance with the provisions of said article twelve, and, if the court so provides, such person shall be eligible for parole in accordance with the provisions of said article twelve in the same manner and with like effect as if such person had been found guilty by the verdict of a jury and the jury had recommended mercy, except that, notwithstanding any provision of said article twelve or any other provision of this code to the contrary, such person shall not be eligible for parole until he or she has served fifteen years.