\[\boxed{\mathbf{15}.}\]
\[1)\ (48 + 93) + 52 =\]
\[= (48 + 52) + 93 = 100 + 93 =\]
\[= 193\]
\[2)\ 374 + 491 + 126 + 509 =\]
\[= (374 + 126) + (491 + 509) =\]
\[= 500 + 1000 = 1500\]