Newt here. Maan, it took me 170 days to fully train a slave. During that time, i maxed out my stats, fully upgraded the mansion, got all the implants and amassed 250k just by just playing cards. Any ideas on how i can train slaves more efficiently? Because 170 days per slave is insane, lmao.
The only way to reduce the training times is to ramp up passive training options. Slave masters can train 4 slaves at a time each, your captain of the guards can train at least 4 guards at a time (probably more, but I limit it to 4 in my games and it definitely has a cap), sending people to the academy can train up various stats, certain jobs can train certain stats, etc. Some stats like stamina can only be trained directly so if you want all your girls to have 100+ stamina so you can fuck them all into oblivion without going unconscious, that's going to take more than a year.
All of the passive training options also have some sort of cap on how high they will train as well (usually 70-120 depending on which option you're looking at). So if you want to train someone up beyond those caps you're going to have to personally homeschool them at that or train them with the dojo depending on the stat.
In my own games, I typically use a combination of slave masters and guard duty to train up everyone to at least 80 melee and ranged, at least 80 discipline, 60 strength, 70 dex, max performance and dancing skill, 60+ corruption, 80ish sex skills, etc. The main skills I have to personally train are stamina on all of my girls, strength, melee and ranged on my main combat team, and survival on my scavengers. Stamina takes by far the longest. I will also typically homeschool certain academic stats on Aria, my accountants, and Nicole, and train medical on everyone so they can get perfectionist via the nurse title.