Find out the missing term of the number series given below.

15, 34, 57, 86, ?, 154

The correct option is 117.

To find the missing term in the given number series, let us analyze the differences between consecutive terms:
15, 34, 57, 86, ?, 154

First, calculate the first-level differences between adjacent numbers:

$34-15=19$

$57-34=23$

$86-57=29$

Notice the sequence of differences obtained so far: 19, 23, 29.
These numbers (19, 23, 29) are consecutive prime numbers.

Following this pattern, the next prime number after 29 is 31.
Therefore, the difference between the missing term and 86 should be 31:

$\text{Missing term}=86+31=117$

To verify the pattern for the next term, the prime number following 31 is 37.
Adding 37 to 117 gives:

$117+37=154$

This matches the last number in the given series (154). Thus, the missing term is 117.