I see from your video that you're failing on the 5.15.alpha1 SQL, and on.
The first one has two SQL statements. Essentially, the statuses for a contribution ("Pending", "Complete", etc.) and for recurring contributions have been the same - but moving forward they'll each have their own list. The two SQL statements create an option group along with values to support this.
Run this SQL: select id, name from civicrm_option_group WHERE name = 'contribution_recur_status';
You should get back one result. If you have no results, that's a problem:
+-----+---------------------------+
| id | name |
+-----+---------------------------+
| 138 | contribution_recur_status |
+-----+---------------------------+
Then run this SQL: select cov.id, cov.option_group_id, cov.name, cov.label, cov.value from civicrm_option_value cov JOIN civicrm_option_group cog ON cov.option_group_id = cog.id WHERE cog.name = 'contribution_recur_status';
You should get back some number of results - I get 12, you may have more:
+------+-----------------+----------------+----------------+-------+
| id | option_group_id | name | label | value |
+------+-----------------+----------------+----------------+-------+
| 1884 | 138 | Completed | Completed | 1 |
| 1885 | 138 | Pending | Pending | 2 |
| 1886 | 138 | Cancelled | Cancelled | 3 |
| 1887 | 138 | Failed | Failed | 4 |
| 1888 | 138 | In Progress | In Progress | 5 |
| 1889 | 138 | Overdue | Overdue | 6 |
| 1890 | 138 | Refunded | Refunded | 7 |
| 1891 | 138 | Partially paid | Partially paid | 8 |
| 1892 | 138 | Pending refund | Pending refund | 9 |
| 1893 | 138 | Chargeback | Chargeback | 10 |
| 1899 | 138 | Processing | Processing | 11 |
| 1900 | 138 | Failing | Failing | 12 |
+------+-----------------+----------------+----------------+-------+
You're also failing on "Fix cache key column name in prev next cache".
That's trying to run this SQL, so also run this command manually:
ALTER TABLE civicrm_prevnext_cache CHANGE COLUMN cacheKey cachekey VARCHAR(255) COMMENT 'Unique path name for cache element of the searched item';