Biber 2.15 cannot find bib files in texmf directory due to a kpsewhich error

[Moritz Wemheuer]

I'd say the fact that

     \documentclass{article}
     \usepackage[backend=biber]{biblatex}
     \addbibresource{{biblatex-examples.bib}}

     \begin{document}
     \cite{sigfridsson}
     \printbibliography
     \end{document}

used to work in biblatex v3.14/Biber 2.14 was accidental. It worked 
because Biber globbed the argument of \addbibresource and apparently the 
globbing rules turned '{biblatex-examples.bib}' into 
'biblatex-examples.bib'.

In biblatex v3.15/Biber 2.15 globbing is no longer on by default 
(because it caused some issues and is probably more confusing than 
useful to the average user). But you can explicitly turn it back on if 
you like.

     \documentclass{article}
     \usepackage[backend=biber]{biblatex}
     \addbibresource[glob]{{biblatex-examples.bib}}

     \begin{document}
     \cite{sigfridsson}
     \printbibliography
     \end{document}

In any case, I'd say the expected/correct/usual input here would use 
only one pair of curly braces

     \documentclass{article}
     \usepackage[backend=biber]{biblatex}
     \addbibresource{biblatex-examples.bib}

     \begin{document}
     \cite{sigfridsson}
     \printbibliography
     \end{document}

Best,
Moritz