Asquare sheet of paper has area $15\text{ cm}^2$. the front side is white and the back side is black. a corner of the sheet is lifted and placed so that the crease is at a $45^\circ$ angle. if the fold is such that the visible black area is equal to the visible white area, how many centimeters long is the crease? express your answer in simplest radical form. [asy] unitsize(2 cm); pair translate = (1.5,0); draw((0); draw(shift(translate)*((1, 1 - sqrt(2/,,, - sqrt(2/3), ; draw((1, 1 - sqrt(2/ - sqrt(2/3),1),dashed); filldraw(shift(translate)*((1 - sqrt(2/3), 1 - sqrt(2/, 1 - sqrt(2/ - sqrt(2/3), ),black); [/asy]