We need three digits numbers.
Since 1+2+3+4+5=15
So, number of possible triplets for multiple of 15 is 1×2×2
so =4×⌊3+4×3−1×2×⌊2=32
Alternate:

divisible by 5=4×3=12

Divisible by 3
12→3,4,5→3!=615→2,3,4→3!=624→1,3,5→3!=642→1,2,3→3!=624
Divisible by 15
1,4,5;4,1,5;3,4,5;4,3,5
Required No. =24+12−4=32