We're dividing 78428217 by 15 
We want to figure out the number of times 78428217 can be divided by 15.

Advancing to step 1:
If we divide 7 by 15, we get 0 and a remainder of 7.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
The remainder is 7 after subtracting 0 from 7.
Bring next digit (8) of the dividend behind the 7 and repeat the process: 78 / 15

Advancing to step 2:
15 can be fit into 78 5 times, resulting in a remainder of 3.
The number 5 becomes the next digit in our result. 
Result so far: 5.0
Deduct 75 from 78 and we're left with 3.
Take the next digit (4) from the dividend and append it to 3, then repeat: 34 / 15

Step 3:
If we divide 34 by 15, we get 2 and a remainder of 4.
The next digit of our result is 2. 
Result so far: 52.0
Subtracting 30 from 34 leaves us with 4.
Grab the next digit (2) from the dividend, add it to 4, then carry on: 42 / 15

Moving on to step 4:
If we divide 42 by 15, we get 2 and a remainder of 12.
Put 2 as the next digit of the answer. 
Result so far: 522.0
Deduct 30 from 42 and we're left with 12.
Include the next digit (8) from the dividend after 12, then repeat: 128 / 15

Moving on to step 5:
The number 15 fits into 128 8 times, leaving a remainder of 8.
Use 8 as the next digit of our solution. 
Result so far: 5228.0
Deduct 120 from 128 and we're left with 8.
Fetch the next digit (2) from the dividend, attach it to 8 and continue: 82 / 15

Moving on to step 6:
15 can be fit into 82 5 times, resulting in a remainder of 7.
The next digit of our result is 5. 
Result so far: 52285.0
Subtracting 75 from 82 leaves us with 7.
Append the next digit (1) from the dividend to 7 and continue with: 71 / 15

Let's proceed to step 7:
71 divided by 15 is 4 with a remainder of 11.
The next digit of our result is 4. 
Result so far: 522854.0
The remainder is 11 after subtracting 60 from 71.
Take the next digit (7) from the dividend and append it to 11, then repeat: 117 / 15

Step 8:
15 can be fit into 117 7 times, resulting in a remainder of 12.
Record the quotient 7 as the next digit in the result. 
Result so far: 5228547.0
Subtracting 105 from 117 leaves us with 12.
Since there are no more digits in the dividend, we add a zero to the remainder making it 120, and continue the process.

Moving on to step 9:
The number 15 fits into 120 8 times, leaving a remainder of 0.
Use 8 as the next digit of our solution. 
Result so far: 5228547.8
Subtract 120 from 120 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 10:
The number 15 fits into 0 0 times, leaving a remainder of 0.
Record the quotient 0 as the next digit in the result. 
Result so far: 5228547.8
Deduct 0 from 0 and we're left 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.

Moving on to step 11:
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: 5228547.8
If we take 0 away from 0, we end up 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.

The final result is 5228547.8 with a remainder of 0.0.