So I've been playing tons and tons of Ashe and assuming laning didn't go to hell and we get to at least mid game, I can usually do decently well.
With that said, how hard is it to transition from playing lots of Ashe to playing Vayne? Is it much harder? Is Ashe one of the "easy" marksmen while Vayne is a difficult marksmen?
Is it going to be a giant leap?
What makes Vayne harder? What makes her hard to play in general?
LostFr0st3 votesThe only thing I'll put here for you is to not auto directly after tumbling with ult on. Too many Vaynes die from "sudden self reveal syndrome" in front of the enemy team. Use the precious stealth pocket.
O Fallen Scholar2 votesYes when this exists 
Buffy4321 votesVayne is atrocious early game, and if you misstep you won't ever get to farm. With how meta Cait and Draven are, you can't ever expect to win trades with her either. Late game, Twitch scales better than Vayne and has an easier laning phase. There's really no reason to play Vayne at all right now.
Ralanr1 votesVayne is harder because she has no way to harass opponents in lane, very weak in lane, and needs items more than others to really start rolling.
A fed Vayne is one of the most powerful things in the game as a result.
HalcyonDweller1 votesThe others said it, Vayne is much harder to get through laning phase with. You will need a support who can mitigate or heal damage up for you, or who can zone the enemy away from you while you farm early game.
PhantomGG1 votesSHORT ANSWER-no, but lane phase sucks.
Explained-The difficult Vayne takes to play is greatly over hyped, you can become decent at her if you one trick her for a whole day. And by a whole day i mean play nothing but Vayne for 12 straight games. Vayne isn't hard to play she is simply ANNOYING to play until you get good at her, and even than she's annoying to play. You lose just about every lane phase match up, unless you have a really good support. If you have a bad support life becomes hell on earth. You pray to god for your team to group so you can have a team fight and get a few kills off it. Than farming on her is misery for unlike all the other adcs she has no way to wave clear and can only hit one minion at a time.
MEGA DETAILED ANSWER
Difficulty tier list for adcs
Generic Adc: 
The first list, is what I call basic generic adcs, these adcs for the most part get their damage from their autos, most the time you see these adcs build crit with the exception for kog. If you can play ashe, you can most likely play jinx, if you can play jinx you can most likely play miss fortune or sivir, the switch is typically easy to make.
Mid Level Adcs: 
These adcs are abit harder to play, they each have their own unique play style that takes abit of time to master, A corci player just can't instantly become a jhin player and a jhin player just can't instantly become a vayne player, it will take time.
The make a name for yourself adcs: 
These 3 are probabbly the most unique adcs in the game, with very unique play styles that no other adc in the game comes close to resembling, because of this they take time to master.
