1.5 is a real number. All numbers that exist on a number line are real numbers, that includes negative numbers.
-<---- -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5 ----->+
Just think of the line x on a x,y coordinate system. Every value of x on that line is a real number. Irrational numbers (surds) are also real. 1.5, 5.6666... They are all real.