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:

Difference between the second and first term:
$34-15=19$

Difference between the third and second term:
$57-34=23$

Difference between the fourth and third term:
$86-57=29$

The differences obtained are 19, 23, and 29. These numbers are consecutive prime numbers starting from 19.

Following this logical pattern, the difference between the fourth term (86) and the missing term should be the next consecutive prime number after 29, which is 31.

Therefore, the missing term is calculated as:
$86+31=117$

To verify this pattern, the difference between the missing term (117) and the last term (154) must be the next prime number after 31, which is 37:

$117+37=154$

Since this matches the final term of the series, the missing term is confirmed to be 117.