Update version to 2.15

[VaishnaviHire]

Description

How Has This Been Tested?

Screenshot or short clip

Merge criteria

• You have read the contributors guide.
• Commit messages are meaningful - have a clear and concise summary and detailed explanation of what was changed and why.
• Pull Request contains a description of the solution, a link to the JIRA issue, and to any dependent or related Pull Request.
• Testing instructions have been added in the PR body (for PRs involving changes that are not immediately obvious).
• The developer has manually tested the changes and verified that the changes work

[grdryn]

/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: grdryn, mattmahoneyrh

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[VaishnaviHire]

/test opendatahub-operator-e2e