CompatHelper: bump compat for FastTransforms to 0.15, (keep existing compat) (#869)

Co-authored-by: CompatHelper Julia <compathelper_noreply@julialang.org>

Author: github-actions[bot]

Project.toml

@@ -35,7 +35,7 @@ Documenter = "0.27"
 DomainSets = "0.3, 0.4, 0.5, 0.6"
 DualNumbers = "0.6.2"
 FFTW = "1"
-FastTransforms = "0.13, 0.14"
+FastTransforms = "0.13, 0.14, 0.15"
 RecipesBase = "1.0"
 Reexport = "1.0"
 SpecialFunctions = "1.1, 2"