Counting distinct lists in a list
Your function is slow because it is O(n2): each element being added to new_seq has to be compared against every previously added element.

To deduplicate a sequence, use a set.  Constructing the set is only O(n) because it uses hashing.

Then, to obtain the size of the set, use len().

def unique(seq):
    return len(set(tuple(element) for element in seq))