Hello :)
a least common multiple, LCM, is the smallest number that all numbers divide evenly into.
To find it you could easily list the multiples of each number.
Multiples of 12:
12, 24, 36, 48, 60, 72, 84
Multiples of 15:
15, 30, 45, 60, 75, 90
The LCM of 12 & 15 would be 60