810999 divided by 15 
The aim is to understand the frequency of 15 in 810999.

On to step 1:
15 can be fit into 8 0 times, resulting in a remainder of 8.
The number 0 becomes the next digit in our result. 
Result so far: 0.0
If we subtract 0 from 8, we get 8.
Fetch the next digit (1) from the dividend, attach it to 8 and continue: 81 / 15

Let's proceed to step 2:
15 can be fit into 81 5 times, resulting in a remainder of 6.
Put 5 as the next digit of the answer. 
Result so far: 5.0
Subtract 75 from 81 to get 6.
Fetch the next digit (0) from the dividend, attach it to 6 and continue: 60 / 15

Moving on to step 3:
The number 15 fits into 60 4 times, leaving a remainder of 0.
Use 4 as the next digit of our solution. 
Result so far: 54.0
Deduct 60 from 60 and we're left with 0.
Append the next digit (9) from the dividend to 0 and continue with: 9 / 15

On to step 4:
15 goes into 9 0 times with a remainder of 9.
The next digit of our result is 0. 
Result so far: 540.0
If we subtract 0 from 9, we get 9.
Take the next digit (9) from the dividend and append it to 9, then repeat: 99 / 15

On to step 5:
The number 15 fits into 99 6 times, leaving a remainder of 9.
Put 6 as the next digit of the answer. 
Result so far: 5406.0
Subtracting 90 from 99 leaves us with 9.
Grab the next digit (9) from the dividend, add it to 9, then carry on: 99 / 15

Advancing to step 6:
If we divide 99 by 15, we get 6 and a remainder of 9.
Write down 6 as next digit of the result. 
Result so far: 54066.0
Subtract 90 from 99 to get 9.
Since there are no more digits in the dividend, we add a zero to the remainder making it 90, and continue the process.

Step 7:
If we divide 90 by 15, we get 6 and a remainder of 0.
Use 6 as the next digit of our solution. 
Result so far: 54066.6
Subtract 90 from 90 to 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.

Step 8:
If we divide 0 by 15, we get 0 and a remainder of 0.
The next digit of our result is 0. 
Result so far: 54066.6
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.

Going ahead to step 9:
15 goes into 0 0 times with a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 54066.6
Subtracting 0 from 0 leaves us with 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 54066.6 and a remainder of 0.0.