The answer is undefined because the question simplifies to 15 ÷ 0, and division by zero is not possible.
Question 2 It depends on how you interpret '='. If you interpret '=' as equality between numbers, then 14 ÷ 0 = 1 ÷ 0 is NOT TRUE because division by zero is undefined (not a number, in other words). If you interpret '=' as a way of saying the same concept, then 14 ÷ 0 = 1 ÷ 0 is true because 14 ÷ 0 and 1 ÷ 0 are different ways of indicating 'undefined'.
Question 3
Many contexts are possible. Consider a plate with zero cookies on it and you want to split up the cookies on the plate into bags with zero cookies in each bag. The number of bags made is the answer to 0 ÷ 0.
How many bags can you make? Make a bag having zero cookies in it. Make another such bag, and another such bag, and another such bag . . . You can keep doing this forever. Thus, the number of bags you can make is infinite, and infinite is a way of saying undefined.