Yes, you can change the figure Pointer property https://www.mathworks.com/help/matlab/ref/matlab.ui.figure-properties.html#d120e354590
You would probably set it to Custom, and you would set PointerShapeCData to a 16 x 16 mask. Use a value of 0 for white, a value of 1 for black, and nan for transparent.
In other words, there is no simple property to just say "scale the pointers to 15 x 15 instead of the default size", but you can use your own bitmap with one row and one column set to nan to have a 15 x 15 effective area.
