Python using glob to get the files and folders.
import glob, os, shutil
# Get all folders in current directory.
folders = [item for item in glob.iglob('*') if os.path.isdir(item)]
# Loop though the folders.
for folder in folders:
    # Check amount of .7z files and if less than 3, remove folder tree.
    if len(glob.glob(folder + r'\*.7z')) < 3:
        shutil.rmtree(folder)
AutoIt using FileFindFirstFile. Could have used STD UDFs which might be less code.
$hFind1 = FileFindFirstFile('*')
If $hFind1 = -1 Then Exit 1
While 1
    ; Get next folder.
    $sFound1 = FileFindNextFile($hFind1)
    If @error Then ExitLoop
    ; Skip files.
    If Not @extended Then ContinueLoop
    ; Find 7z files.
    $hFind2 = FileFindFirstFile($sFound1 & '\*.7z')
    ; If no handle, delete folder.
    If $hFind2 = -1 Then
        DirRemove($sFound1)
        ContinueLoop
    EndIf
    ; Count for 7z files.
    $iCount = 0
    ; Get count of 7z files.
    While 1
        $sFound2 = FileFindNextFile($hFind2)
        If @error Then ExitLoop
        $iCount += 1
    WEnd
    FileClose($hFind2)
    ; Remove folder if count less than 3.
    If $iCount < 3 Then
        DirRemove($sFound1, 1); 1 = recurse
    EndIf
WEnd
FileClose($hFind1)