Decrease Perceived Complexity threshold to 15

What does this MR do?

• refactor app/models/event.rb:242:3
• decrease Perceived Complexity threshold to 15

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

It's second step for #31358 (moved)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

#31358 (moved)

/cc @rymai @markglenfletcher @grzesiek @blackst0ne @rspeicher

Possible labels: Community Contribution backstage Edge static analysis