Bump u/xp to v1.15.0-up.1.rc.3

[phisco]

Description of your changes

As part of https://github.com/upbound/universal-crossplane/issues/428.

I have:

• [x] Read and followed Upbound's contribution process.
• [x] Run make reviewable to ensure this PR is ready for review.
• [x] Added backport release-x.y labels to auto-backport this PR, as appropriate.

How has this code been tested