Specifically methylates the guanosine in position 1516 of 16S rRNA. guanosine(1516) in 16S rRNA + S-adenosyl-L-methionine = H(+) + N(2)-methylguanosine(1516) in 16S rRNA + S-adenosyl-L-homocysteine Belongs to the methyltransferase superfamily. RsmJ family.