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

[github-actions[bot]]

This pull request changes the compat entry for the Interpolations package from 0.9, 0.10, 0.11, 0.12, 0.13, 0.14 to 0.9, 0.10, 0.11, 0.12, 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.

[mkitti]

Please merge this. Let me know if there is an issue.

[devmotion]

Tests seem to pass but I'm unsure what the breaking change in 0.15 was?

[mkitti]

Interpolations.jl dropped support for Julia before Julia 1.6. We stopped testing against Julia 1.3 due ChainRulesCore.jl compatability.

https://github.com/JuliaMath/Interpolations.jl/pull/566#issuecomment-1819813909