30.
30
The LCM (Least Common Multiple) of 115 and 15 is 345. The prime factors of 115 are 5 and 23. The prime factors of 15 are 3 and 5. Multiply the smallest encountered number of same factors, 3, 5, and 23, to get 345.
In this case, the one that has the least digits.
5, 10, 15 and 20 have five as a factor. The number 16 has five factors.
The smallest number with exactly 36 factors is 1260. The factors are: 1, 2, 3, 4, 5, 6, 7, 9, 10, 12, 14, 15, 18, 20, 21, 28, 30, 35, 36, 42, 45, 60, 63, 70, 84, 90, 105, 126, 140, 180, 210, 252, 315, 420, 630, and 1260.