Step 1 :The spinner has 15 regions, so there are 15 possible outcomes.
Step 2 :The even numbers from 1 to 15 are 2, 4, 6, 8, 10, 12, 14, and the multiples of 3 are 3, 6, 9, 12, 15.
Step 3 :We can see that 6 and 12 are both even numbers and multiples of 3, so we should not count them twice.
Step 4 :Therefore, the favorable outcomes are 2, 4, 6, 8, 10, 12, 14, 3, 9, 15, a total of 10 outcomes.
Step 5 :The probability is the number of favorable outcomes divided by the total number of outcomes, which is \(\frac{10}{15} = \frac{2}{3}\).
Step 6 :Final Answer: The probability that the spinner will stop on an even number or a multiple of 3 is \(\boxed{\frac{2}{3}}\).