  We present a new analysis of the diffuse soft $\gamma$-ray emission towards
the inner Galaxy as measured by the SPectrometer aboard the INTEGRAL satellite
(SPI) with 16 years of data taking. The analysis implements a spatial template
fit of SPI data and an improved instrumental background model. We characterize
the contribution of Primordial Black Holes (PBH) as dark matter (DM) candidates
evaporating into $\mathcal{O}$(1) MeV photons by including, for the first time,
the spatial distribution of their signal into the fitting procedure. No PBH
signal is detected, and we set the strongest limit on PBH DM for masses up to
$4 \times 10^{17}$ g, significantly closing in into the so-called asteroid mass
range.
