The addition of 12 and 15 is:

$12 + 15 = 27$

Would you like more details or have any questions about this?

Here are five related questions to explore:

1. What is the sum of 27 and 18?
2. How would you subtract 15 from 27?
3. Can you add 12, 15, and 20 together?
4. What is the difference between 30 and 12?
5. How do you find the sum of multiple numbers?

Tip: When adding numbers, grouping them into tens or using a number line can help make the process quicker!