  We present multi-epoch, parsec-scale core brightness temperature observations
of 447 AGN jets from the MOJAVE and 2cm Survey programs at 15 GHz from 1994 to
2019. The brightness temperature of each jet over time is characterized by its
median value and variability. We find that the range of median brightness
temperatures for AGN jets in our sample is much larger than the variations
within individual jets, consistent with Doppler boosting being the primary
difference between the brightness temperatures of jets in their median state.
We combine the observed median brightness temperatures with apparent jet speed
measurements to find the typical intrinsic Gaussian brightness temperature of
(4.1 +- 0.6)*10^10 K, suggesting that jet cores are at or below equipartition
between particle and magnetic field energy in their median state. We use this
value to derive estimates for the Doppler factor for every source in our
sample. For the 309 jets with both apparent speed and brightness temperature
data, we estimate their Lorentz factors and viewing angles to the line of
sight. Within the BL Lac optical class, we find that high-synchrotron-peaked
(HSP) BL Lacs have smaller Doppler factors, lower Lorentz factors, and larger
angles to the line of sight than intermediate and low-synchrotron-peaked (LSP)
BL Lacs. We confirm that AGN jets with larger Doppler factors measured in their
parsec-scale radio cores are more likely to be detected in gamma rays, and we
find a strong correlation between gamma-ray luminosity and Doppler factor for
the detected sources.
