We look at the division of 551439 by 15 
The aim is to understand the frequency of 15 in 551439.

Step 1:
When dividing 5 by 15, we get 0 with a remainder of 5.
Put 0 as the next digit of the answer. 
Result so far: 0.0
Deduct 0 from 5 and we're left with 5.
Bring next digit (5) of the dividend behind the 5 and repeat the process: 55 / 15

Advancing to step 2:
55 divided by 15 is 3 with a remainder of 10.
Write down 3 as next digit of the result. 
Result so far: 3.0
Deduct 45 from 55 and we're left with 10.
Append the next digit (1) from the dividend to 10 and continue with: 101 / 15

Advancing to step 3:
If we divide 101 by 15, we get 6 and a remainder of 11.
Record the quotient 6 as the next digit in the result. 
Result so far: 36.0
Subtract 90 from 101 to get 11.
Append the next digit (4) from the dividend to 11 and continue with: 114 / 15

On to step 4:
If we divide 114 by 15, we get 7 and a remainder of 9.
Use 7 as the next digit of our solution. 
Result so far: 367.0
Deduct 105 from 114 and we're left with 9.
Append the next digit (3) from the dividend to 9 and continue with: 93 / 15

Let's proceed to step 5:
When dividing 93 by 15, we get 6 with a remainder of 3.
The next digit of our result is 6. 
Result so far: 3676.0
If we take 90 away from 93, we end up with 3.
Fetch the next digit (9) from the dividend, attach it to 3 and continue: 39 / 15

On to step 6:
The number 15 fits into 39 2 times, leaving a remainder of 9.
Use 2 as the next digit of our solution. 
Result so far: 36762.0
Subtracting 30 from 39 leaves us with 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Going ahead to step 7:
15 can be fit into 90 6 times, resulting in a remainder of 0.
Use 6 as the next digit of our solution. 
Result so far: 36762.6
If we subtract 90 from 90, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Let's proceed to step 8:
15 can be fit into 0 0 times, resulting in a remainder of 0.
Write down 0 as next digit of the result. 
Result so far: 36762.6
The remainder is 0 after subtracting 0 from 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

Step 9:
0 divided by 15 is 0 with a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 36762.6
If we subtract 0 from 0, we get 0.
Since there are no more digits in the dividend, we add a zero to the remainder making it 0, and continue the process.

After the division, we end up with 36762.6 and a remainder of 0.0.