Error in size inputs scalar

can somebody tell me why I am getting an error called' Error using zeros. Size inputs must be scalar' for the below first code.

x=5:1:15;

y=5:1:15;

z=5:1:15;

B=zeros(x,y,z);

And If Give the inputs like below no errors.But I want to simplify the code.

x=5,6,7,8,9,10,11,12,13,14,15;

y=5,6,7,8,9,10,11,12,13,14,15;

z=5,6,7,8,9,10,11,12,13,14,15;

B=zeros(x,y,z);