The given sequence is 5,6,8,11,15
The first step is to analyse the pattern in the sequence.
5 + 1 = 6
6 + 2 = 8
8 + 3 = 11
11 + 4 = 15
We can see that the numbers being added to each term is increasing by 1. This means that the next number to be added to 15 to get the next term is 5. Thus
next term = 15 + 5
next term or number = 20