When raising your vice stat, you need to make sure that you take actions which have lower vice ceilings since those actions stop giving vice at a certain point. The vice ceiling seems to be 10 above the amount of vice needed to take the action. So, take actions with a 10 from 15 until you reach 20, and actions with 15 until you reach 25.
The quest Nothing but the truth has a very large amount of vice to gain if you betray Lorraine and notably has enough checks to get you from 22 vice to 26 since it has checks that require 14, 15 and 17 vice and seems to give one bonus vice, so do that before the second Paulina and the reverse summoning ritual red fires which require 20. I did it at 22 which got me up to 26. I got to 27 with Paulina and then did the reverse summoning ritual and absorbed the three red flames which pushed me to the goal at 30 but you can do whichever order for the final four.
Stealing should get you up to 10, and possibly even 15. There are plenty of ropes , apples and chests to steal from. You will also find places on your own to gain vice points from 10 to 15 using choices that require 5 vice.
Some well hidden vice actions that I found:
10 vice: (gets you from 15 to 20)
Selling out Paulina in the maid academy
Leaving the apprentice to die in the Swamp
Doing Rotten Love by not slaying the demon
Doing Homewrecking by choosing Slander
Selling out Charlotte to Victor after you reach 10 Infamy
Selling out the Twins in Demon-Cracy on the shadow route.
15 vice: (gets you from 20 to 25)
Investing with the slave trader in the Entertainment den,
Deliberately losing at Slay the Demon in the Entertainment den
17 vice: (gets you up to 26)
Enslaving Lorraine in Nothing but the truth
20 vice: ( Gets you from 26 to 30)
Selling out Paulina again in the maid academy
3x red flames in the reverse summoning ritual
Be careful not to lose Auras Virginity to George (or anyone else) while you do this. I did it on story mode to avoid having to risk advancing inside Aura further than necessary to gain vice and theft.