Glad you got it working, but there's another approach you might want to consider rather than nested IFs in a situation like this.
Create a table on another sheet or elsewhere on your sheet with your levels and the score needed to reach them:
0 Level 1
4 Level 2
8 Level 3
12 Level 4
15 Level 5
Then use a VLOOKUP or an INDEX(MATCH function to find matches. I like the INDEX(MATCH since it gives you more control.
=INDEX(Sheet1!$B$1:$B$5,MATCH(A1,Sheet1!$A$1:$A$5,1))
In this case, our list would be on Sheet1, with the Levels listed in column B and the required scores in column A, while our formula is on sheet 2 referencing actual scores that start in A1.
The INDEX function looks at an array - B1:B5 - and returns a value from a specified row in that array. The MATCH function looks at an array - A1:A5 - and returns the location in the array of the highest number that is less than or equal to the match value. It passes this result back to the INDEX so it can select the appropriate row.
This method is easier to maintain, modify and expand than a multi-level nested IF.