  For seven decades by A-15 superconductors we meant metallic $A_3B$ alloys
(where A is a transition metal, and B is groups IIIB and IVB element)
discovered by Hardy and Hulm (Phys. Rev. 89, 884 (1953)). Nb3Ge exhibited the
highest superconducting transition temperature, $T_c = 23 K$, among these
alloys. One of these alloys, $Nb_3Sn$, is primary material in modern applied
superconductivity. Recently Guo et al (arXiv:2307.13067) extended the family of
superconductors where the metallic ions arranged in the beta tungsten (A-15)
sublattice by observation of $T_{c,zero} = 81 K$ in $La_4H_{23}$ phase
compressed at $P = 118 GPa$. Despite the $La_4H_{23}$ has much lower $T_c$ in
comparison with near-room-temperature superconducting $LaH_{10}$ phase
($T_{c,zero} = 250 K$ at $P = 200 GPa$) discovered by Drozdov et al (Nature
569, 531 (2019)), the $La_4H_{23}$ holds the record high $T_c$ within A-15
family. Cross et al (Phys. Rev. B 109, L020503 (2024)) confirmed the
high-temperature superconductivity in the compressed $La_4H_{23}$. In this
paper, we analyzed available experimental data measured in $La_4H_{23}$ and
found that this superconductor exhibits nanograined structure, 5.5 nm < D < 35
nm, low crystalline strain < 0.003, high electron-phonon coupling constant, 1.5
< $\lambda_{e-ph}$ < 2.55, and moderate level of the nonadiabaticity
$\Theta_{D}/T_{F}$. We found that derived $\Theta_{D}/T_{F}$ and $T_c/T_F$
values for the $La_4H_{23}$ phase are similar to the ones in cuprates,
pnictides, and near-room-temperature superconductors $H_3S$ and $LaH_{10}$,
which implies that the $La_4H_{23}$ phase falls to unconventional
superconductors band in the Uemura plot.
