Available in limited colors. 15 inches?  Why, you ask?  We're glad you asked!   For many magicians, an 18" silk is too large for a thumb tip and when you start adding multiple 18" silks, many times you can't get the number you're looking for into the device you're using.  Going down to 12 inches makes for a much smaller silk.   When you do the math, it's quite clear:  12" silks are 144 square inches.   15" are 225 square inches.  18" are 324 square inches.