The given sequence is 12, 15, 22, 26. By observing the pattern, we can see that each number is obtained by adding a certain value to the previous number. The first number is increased by 3 to get the second number (12 + 3 = 15). The second number is increased by 7 to get the third number (15 + 7 = 22). Similarly, the third number is increased by 4 to get the fourth number (22 + 4 = 26). Therefore, the next number in the sequence would be obtained by adding 4 to the previous number, resulting in 26.