+118612 Do you mean, does
$$-\sqrt{15}=\sqrt{-15}\quad?$$
No it does not. 
No real number multiplied by itself can give a negative answer so there are no Real answers to $${\sqrt{-{\mathtt{15}}}}$$
however there is another whole number system with imaginary numbers and the most basic imaginary number is $${\sqrt{-{\mathtt{1}}}}$$ it is called $${i}$$
$${\sqrt{-{\mathtt{15}}}}$$ = $${\sqrt{{\mathtt{15}}}}{\mathtt{\,\times\,}}{i}$$
+118612 Do you mean, does
$$-\sqrt{15}=\sqrt{-15}\quad?$$
No it does not.
No real number multiplied by itself can give a negative answer so there are no Real answers to $${\sqrt{-{\mathtt{15}}}}$$
however there is another whole number system with imaginary numbers and the most basic imaginary number is $${\sqrt{-{\mathtt{1}}}}$$ it is called $${i}$$
$${\sqrt{-{\mathtt{15}}}}$$ = $${\sqrt{{\mathtt{15}}}}{\mathtt{\,\times\,}}{i}$$
