Update dependency Django to v2.2.15

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
Django (source, changelog)	patch	==2.2.14 -> ==2.2.15

---

Release Notes

django/django

### [`v2.2.15`](https://togithub.com/django/django/compare/2.2.14...2.2.15) [Compare Source](https://togithub.com/django/django/compare/2.2.14...2.2.15)

---

Renovate configuration

:date: Schedule: At any time (no schedule defined).

:vertical_traffic_light: Automerge: Disabled by config. Please merge this manually once you are satisfied.

:recycle: Rebasing: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

:no_bell: Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by WhiteSource Renovate. View repository job log here.