Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Year | Conservative\ncouncillors | Labour\ncouncillors | Independent\ncouncillors | Liberal\ncouncillors |
| --- | --- | --- | --- | --- |
| 1947 | 3 | 2 | 18 | 1 |
| 1951 | 5 | 2 | 17 | 0 |
| 1952 | 3 | 3 | 18 | 0 |
| 1953 | 4 | 3 | 17 | 0 |
| 1954 | 3 | 4 | 17 | 0 |
| 1955 | 2 | 5 | 17 | 0 |
| 1956 | 2 | 6 | 16 | 0 |
| 1957 | 2 | 5 | 17 | 0 |
| 1958 | 2 | 6 | 16 | 0 |
| 1960 | 2 | 5 | 16 | 1 |
| 1961 | 2 | 5 | 15 | 2 |
| 1963 | 2 | 6 | 12 | 4 |
| 1964 | 3 | 6 | 11 | 4 |
| 1965 | 4 | 5 | 11 | 3 |
| 1966 | 9 | 4 | 6 | 5 |
| 1967 | 9 | 4 | 9 | 2 |
| 1972 | 10 | 10 | 3 | 1 |
Question:
how many years had at least 15 or more independent councillors?
Answer:
11