| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [prep] 15 years ' | 22 |
|
| 2 | [prep] 15 years ' | 22 |
|
| 3 | to 15 years ' | 11 |
|
| 4 | to 15 years ' | 11 |
|
| 5 | of 15 years ' | 6 |
|
| 6 | of 15 years ' | 6 |
|
