  We present the main results from a long-term reverberation mapping campaign
carried out for the Seoul National University Active Galactic Nuclei (AGN)
Monitoring Project. High-quality data were obtained during 2015-2021 for 32
luminous AGNs (i.e., continuum luminosity in the range of $10^{44-46}$ erg
s$^{-1}$) at a regular cadence, of 20-30 days for spectroscopy and 3-5 days for
photometry. We obtain time lag measurements between the variability in the
H$\beta$ emission and the continuum for 32 AGNs; twenty-five of those have the
best lag measurements based on our quality assessment, examining correlation
strength, and the posterior lag distribution. Our study significantly increases
the current sample of reverberation-mapped AGNs, particularly at the moderate
to high luminosity end. Combining our results with literature measurements, we
derive a H$\beta$ broad line region size--luminosity relation with a shallower
slope than reported in the literature. For a given luminosity, most of our
measured lags are shorter than the expectation, implying that single-epoch
black hole mass estimators based on previous calibrations could suffer large
systematic uncertainties.
