Update otel4s to 0.15.0 and otel4s-sdk to 0.16.0

[iRevive]

Before submitting pull request:

• Check if the project compiles by running sbt compile
• Verify docs compilation by running sbt compileDocs
• Check if tests pass by running sbt test
• Format code by running sbt scalafmt

[iRevive]

Since otel4s is still pre-1.0, could you please release a new version once you merge this MR?

[iRevive]

Resolves #2773, #2774.