$a)$

$3\frac{2}{15}+4\frac{14}{15}=7\frac{16}{15}=8\frac{1}{15}$

$b)$

$5\frac{1}{15}+2\frac{11}{15}=7\frac{12}{15}$

$c)$

$2\frac{7}{12}+4\frac{9}{12}=6\frac{16}{12}=7\frac{4}{12}=7\frac{1}{3}=7\frac{5}{15}$

$d)$

$6\frac{5}{12}+\frac{11}{12}=6\frac{16}{12}=7\frac{4}{12}=7\frac{1}{3}=7\frac{5}{15}$

$8\frac{1}{15}>7\frac{12}{15}>7\frac{5}{15}=7\frac{5}{15}$