correct pager pagination and add reasonable default value (15) 

correct pager pagination and add reasonable default value (15)  to prevent too many pages from showing.fixes #1902

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #1902
| Refs tickets  | -
| License       | MIT
| Doc PR        | -