CompatHelper: bump compat for Interpolations to 0.15, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Interpolations package from 0.13, 0.14 to 0.13, 0.14, 0.15.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.50%. Comparing base (ae82eb5) to head (d20b892).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #18   +/-   ##
=======================================
  Coverage   94.50%   94.50%           
=======================================
  Files           3        3           
  Lines          91       91           
=======================================
  Hits           86       86           
  Misses          5        5           

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