Triangle $ABC$ and triangle $DEF$ are congruent, isosceles right triangles. The square inscribed in triangle $ABC$ has an area of 15 square centimeters. What is the area of the square inscribed in triangle $DEF$? Express your answer as a common fraction.

[asy]
draw((0,0)--(2,0)--(0,2)--(0,0)--cycle,linewidth(2));
draw((0,0)--(1,0)--(1,1)--(0,1)--(0,0)--cycle,linewidth(2));
draw((1/8,0)--(1/8,1/8)--(0,1/8),linewidth(1));

draw((3,0)--(5,0)--(3,2)--(3,0)--cycle,linewidth(2));
draw((3+2/3,0)--(3+4/3,2/3)--(3+2/3,4/3)--(3,2/3)--(3+2/3,0)--cycle,linewidth(2));
draw((3+1/8,0)--(3+1/8,1/8)--(3,1/8),linewidth(1));

label("A",(0,2),NW);
label("B",(0,0),SW);
label("C",(2,0),SE);

label("D",(3,2),NW);
label("E",(3,0),SW);
label("F",(5,0),SE);

[/asy]
[asy]
fill((0,0)--(1,0)--(1,1)--(0,1)--cycle, gray);
draw((0,0)--(2,0)--(0,2)--cycle, linewidth(2));
draw((0,0)--(1,0)--(1,1)--(0,1)--cycle, linewidth(2));
draw((0,0)--(1,1), linewidth(2));
label("A",(0,2),NW);
label("B",(0,0),SW);
label("C",(2,0),SE);

fill((3+2/3,0)--(3+4/3,2/3)--(3+2/3,4/3)--(3,2/3)--cycle, gray);
draw((3,0)--(5,0)--(3,2)--cycle, linewidth(2));
draw((3+2/3,0)--(3+4/3,2/3)--(3+2/3,4/3)--(3,2/3)--cycle, linewidth(2));
draw((3,4/3)--(3+2/3,4/3)--(3+2/3,0), linewidth(2));
draw((3,2/3)--(3+4/3,2/3)--(3+4/3,0), linewidth(2));
label("D",(3,2),NW);
label("E",(3,0),SW);
label("F",(5,0),SE);
[/asy] In the diagram above, we have dissected triangle $ABC$ into four congruent triangles. We can thus see that the area of triangle $ABC$ is twice the area of its inscribed square, so its area is $2(15) = 30$ sq cm. In the diagram on the right, we have dissected triangle $DEF$ into nine congruent triangles. We can thus see that the area of the inscribed square is $4/9$ the area of triangle $DEF$. The area of triangle $DEF$ is 30 sq cm (since it's congruent to triangle $ABC$), so the area of the square is $(4/9)(30) = \boxed{\frac{40}{3}}$ sq cm.