How To Go About This
So, for now, I'm gonna ignore the influence of hero into this by expecting you to have at least the amount or more hero than the prime level of choice. So what we want to know now is how the prime levels scale. For this, we just go into the prime levels at different difficulties and look for changes. I think many people already know that you'll notice two big changes.
 The enemies take longer to defeat
 You die faster
These two aspects should instantly bring up a few questions in our minds. The simplest of all those questions is the why. If the enemies take longer to defeat it means one or several things. For example, they could have more health or we do less damage. It could also be both. For the second aspect, it's most likely because the enemies deal more damage.
So let's compare the health and damage of the enemies on the different prime levels starting with prime level zero. Once we got our data we start to compare it to prime level zero and additionally we could also look at the steps between each prime level.
Collecting Data
Okay, so no joke. I literally went into the infestation expedition on prime level zero to 15 and checked the health of the same mob over and over again and let myself getting hit by the same attack of this enemy over and over. The enemy of my choice was the Lashing Terror. I noted down all the values in a spreadsheet. So you get two tables, one of the
Enemy Health
Prime Level 
0

1

2

3

4

5

6

7

8

9

10

Health  36533  41648  45302  49320  56627  61742  67222  73433  84024  91700  100102 
Prime Level 
11

12

13

14

15


Health  109236  124946  136271  148693  162210 
and one of the
Enemy Damage
Prime Lvl  Avg. Dmg  Damage...  
0  1231.4  1298  1212  1284  1270  1278  1196  1206  1170  1143  1257  
1  1430.8  1388  1443  1369  1370  1456  1488  1440  1447  1427  1480  
2  1531.5  1623  1561  1552  1563  1542  1528  1455  1428  
3  1652.82  1715  1622  1722  1652  1614  1716  1652  1694  1589  1599  1606  
4  1910.92  2002  1955  1884  1997  1911  1977  1902  1917  1815  1873  1852  1846 
A bit weird that I only collected data on the damage from prime 0 to prime 4. Well, it's not just random but more on that later.
Evaluation of Data
So the next step is to evaluate our data. So we want to know how the prime levels scale. To figure this out we assume prime level zero is our base health and damage. So 100%. To determine how prime level 1 scaled we divide its health through the base health. We do the same with the damage.
This means in prime level 1 the enemies have 41648 / 36533 = 1.1400 or 114.00% the health.
Doing the same with the average damage we get 1430.8 / 1231.4 = 1.1619 or 116.19% damage.
So let's do this for every case we divide its health and average damage through the health and average damage on prime level zero. Now we get the following table.
Prime Level  Health  Percentage  Average Damage  Percentage 
0  36533  100%  1231.4  100% 
1  41648  114.00%  1430.8  116.19% 
2  45302  124.00%  1531.5  124.37% 
3  49320  135.00%  1652.82  134.22% 
4  56627  155.00%  1910.92  155.18% 
5  61742  169.00%  
6  67222  184.00%  
7  73433  201.00%  
8  84024  229.99%  
9  91700  251.01%  
10  100102  274.00%  
11  109236  299.01%  
12  124946  342.01%  
13  136271  373.01%  
14  148693  407.01%  
15  162210  444.01% 
You may notice that I realized after prime level four that the damage most likely scales just like the health of the enemies do. It's too similar to be a coincidence. Even though to be certain one should've done it through this is enough evidence to me. Aside from knowing now that on prime level 13 the enemies do almost 4 times the damage and have almost 4 times the health.
Next, let's see if it scales linearly. We can do this by dividing the current enemy's health on the prime level through the previous one. So for prime level 2, it would be 45302 / 41648 = 1.0877 or 108.77%. We want the increase between the first and the second unrelated to the previous one. So we need to get 100% out of it. We can simply do this by subtracting one. Which means we get 1.0877  1 = 0.0877 or 8.77%
Prime Level 
0

1

2

3

4

5

6

7

8

9

10

Health  36533  41648  45302  49320  56627  61742  67222  73433  84024  91700  100102 
% 


14.00%

8.77%

8.89%

14.82%

9.03%

8.88%

9.24%

14.42%

9.14%

9.16%

Prime Level 
11

12

13

14

15


Health  109236  124946  136271  148693  162210  
% 
9.12%

14.38%

9.06%

9.12%

9.09%

As you can see the increase is not linear. Now the question is raised whether or not this is fixed percentages set by the developers or if they use a nonlinear function. To figure this out we need to find a pattern. Though that's not something I'm gonna do today, because I have to get ready for the flight to Paris and stuff.
"So hope you enjoy the data, GreenyNeko out!"
~GreenyNeko