[tex]\displaystyle\bf\\a_{1}=15\\\\d=2\\\\S_{30} =?\\\\\\a_{30} =a_{1} +29d=15+29\cdot 2=15+58=73\\\\\\S_{30}=\frac{a_{1} + a_{30} }{2}\cdot 30=(a_{1} + a_{30} )\cdot 15=(15+73)\cdot 15=\\\\\\=88\cdot 15=1320[/tex]