To install GLIBC_2.14 or GLIBC_2.15, download package from /gnu/libc/ index at
Then follow instructions listed by Timo:
For example glibc-2.14.tar.gz in your case.
tar xvfz glibc-2.14.tar.gz
cd glibc-2.14
mkdir build
cd build
../configure --prefix=/opt/glibc-2.14
make
sudo make install
export LD_LIBRARY_PATH=/opt/glibc-2.14/lib:$LD_LIBRARY_PATH