  The nuclear level density of $^{115}$Sn has been measured in an excitation
energy range of $\sim $2 - 9 MeV using the experimental neutron evaporation
spectra from the $^{115}$In($p,n$)$^{115}$Sn reaction. The experimental level
densities were compared with the microscopic Hartree-Fock BCS (HFBCS),
Hartree-Fock-Bogoliubov plus combinatorial (HFB+C), and an exact pairing plus
independent particle model (EP+IPM) calculations. It is observed that the
EP+IPM provides the most accurate description of the experimental data. The
thermal properties (entropy and temperature) of $^{115}$Sn have been
investigated from the measured level densities. The experimental temperature
profile as well as the calculated heat capacity show distinct signatures of a
transition from the strongly-paired nucleonic phase to the weakly paired one in
this nucleus.
