For a quick push, I think Morgan would be a better pick.The NG+ and thus I assume also the gallery will be unlocked once you have had a single playthrough not using the built-in cheats on your phone. If you were able to use a save game editor or RenPy console commands without breaking the save, the game will not notice that. It only sets a flag once you opened the in game menu.
And once you unlocked the NG+ feature and thus the gallery, it will probably stay unlocked even if you cheat on later playthroughs. It may just be that not everything carries over into NG+ but it will stay your old one.
So if you don't care about anything and are happy with the in game cheats but want to unlock the gallery, your best option probably is a quick Bree or Sasha run - ignore everybody else, get married, boom: unlock.
Her mission process is simple, and her schedule is also very fixed. There is only one mission that needs to wait for her to call, and the whole process does not cost much money. If you simply want to advance quickly, I highly recommend finding Morgan.
But for the contents of the Gallery, I am not sure what is used to calculate the unlocking. Some of the unlocked content in it is what I have already played, and some of the unlocked content is the route I did not choose. So if it is really based on sex Judging by experience, it is amazing.
I hope it’s just that it’s not fully developed, and some content is still locked. If you have to play the content to unlock it, or you need to judge it based on certain data, it will be very troublesome. It will even make players look forward to Cheat all unlock function or begging others to share files.