How compatible are different versions of glibc?

There are only minor binary compatibility issues between glibc 2.14 and glibc 2.15 according to the report from the Linux upstream tracker.

The report is generated by the abi-compliance-checker and abi-tracker tools.

See also https://sourceware.org/glibc/wiki/Testing/ABI_checker.

Please use ABI compliance checker for checking compatibility of libraries.

In general, running binaries that were compiled for an older glibc version (e.g. 2.13) will run fine on a system with a newer glibc (e.g. 2.14, like your system).

Running a binary that was built for a newer glibc (e.g. 2.15, like the one that fails) on a system with an older glibc will probably not work.

In short, glibc is backward-compatible, not forward-compatible.