I'm experimentally rebuilding rawhide with the not-yet-released GCC 15 to see if anything breaks, and to help write the porting guide.  See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15

My test build with GCC 15 failed:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed/build/8476036/

whereas my test build with GCC 14 succeeded:
https://copr.fedorainfracloud.org/coprs/dmalcolm/gcc-15-smoketest-3.failed.checker/build/8477629/

Looking at the failure logs e.g.
https://download.copr.fedorainfracloud.org/results/dmalcolm/gcc-15-smoketest-3.failed/fedora-rawhide-x86_64/08476036-Macaulay2/builder-live.log.gz
I see:

In file included from /usr/include/recint/rdiv.h:48,
                 from /usr/include/recint/rint.h:53,
                 from /usr/include/givaro/modular-ruint.h:24,
                 from /usr/include/givaro/modular.h:26,
                 from ../../linbox/field/field-traits.h:30,
                 from ../../linbox/solutions/methods.h:25,
                 from ../../linbox/algorithms/rational-solver.h:41,
                 from ../../linbox/algorithms/diophantine-solver.h:29,
                 from diophantine-solver.C:26:
/usr/include/recint/rfiddling.h: In static member function 'static RecInt::rint<K> RecInt::rint<K>::maxFFLAS()':
/usr/include/recint/rfiddling.h:170:29: error: 'class RecInt::rint<K>' has no member named 'Low' [-Wtemplate-body]
  170 |         set_highest_bit(max.Low.Value);
      |                             ^~~

See https://fedoraproject.org/wiki/User:Dmalcolm/gcc-15#C++:_error_with_-Wtemplate-body for notes.

Reproducible: Didn't try