We look at the division of 623618 by 15 
The aim is to understand the frequency of 15 in 623618.

Advancing to step 1:
The number 15 fits into 6 0 times, leaving a remainder of 6.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 6 and we're left with 6.
Bring next digit (2) of the dividend behind the 6 and repeat the process: 62 / 15

Advancing to step 2:
When dividing 62 by 15, we get 4 with a remainder of 2.
Record the quotient 4 as the next digit in the result. 
Result so far: 4.0
The remainder is 2 after subtracting 60 from 62.
Take the next digit (3) from the dividend and append it to 2, then repeat: 23 / 15

On to step 3:
The number 15 fits into 23 1 times, leaving a remainder of 8.
Put 1 as the next digit of the answer. 
Result so far: 41.0
If we subtract 15 from 23, we get 8.
Take the next digit (6) from the dividend and append it to 8, then repeat: 86 / 15

Advancing to step 4:
15 goes into 86 5 times with a remainder of 11.
The number 5 becomes the next digit in our result. 
Result so far: 415.0
Subtract 75 from 86 to get 11.
Bring next digit (1) of the dividend behind the 11 and repeat the process: 111 / 15

Advancing to step 5:
15 goes into 111 7 times with a remainder of 6.
Use 7 as the next digit of our solution. 
Result so far: 4157.0
Subtracting 105 from 111 leaves us with 6.
Bring next digit (8) of the dividend behind the 6 and repeat the process: 68 / 15

On to step 6:
If we divide 68 by 15, we get 4 and a remainder of 8.
Record the quotient 4 as the next digit in the result. 
Result so far: 41574.0
If we subtract 60 from 68, we get 8.
Since there are no more digits in the dividend, we add a zero to the remainder making it 80, and continue the process.

Going ahead to step 7:
The number 15 fits into 80 5 times, leaving a remainder of 5.
The next digit of our result is 5. 
Result so far: 41574.5
The remainder is 5 after subtracting 75 from 80.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Step 8:
15 can be fit into 50 3 times, resulting in a remainder of 5.
Record the quotient 3 as the next digit in the result. 
Result so far: 41574.53
The remainder is 5 after subtracting 45 from 50.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

Going ahead to step 9:
15 can be fit into 50 3 times, resulting in a remainder of 5.
Use 3 as the next digit of our solution. 
Result so far: 41574.533
If we take 45 away from 50, we end up with 5.
Since there are no more digits in the dividend, we add a zero to the remainder making it 50, and continue the process.

The final outcome is 41574.533, with a leftover of 0.0005.