As a tickling and other erotica writer your question is one that any writer needs to ask. I do when I sit down to write something.
The first thing that matters is the structure of your story, and the impact that you wish to convey. A lot of people,to be blunt, are looking for something to get off on, and they are going to be searching for short form, and they are going to want a lot of Ha-Ha's off the top and all thru. Else they will move onto the next. But, many people are looking for longer form, where you feel a connection or sympathy with the characters. This style requires that you layer in a measure of character development. Unless you are writing a serial, the only way to do this is to layer in the development off the top. Thus a longer intro. You can cheat around this with a flash forward, or memory scene within the intro, but mostly you have to do the writing work to lay in the info.
The best thing to do is write the entire piece then go back and judge your intro. Is it worth the investment to a reader for the payoff? Is all of it needful to the story? Do the readers need it all to proceed? Edit as needed. Trying to judge it without a full context is hard, and not a great way to go in my opinion. Without the rest of the tale, you can't tell if the stuff in the intro is needful, or even in need of being expanded.
Most importantly, as Cosmo said, write your own story. The one you want to tell. If it's good, the audience will find it. Once you start to pander to your audience then you are starting to compromise the tale you are telling.
Myriads