First off, I hate people suggesting the fiber idea. Having quick crap does not mean you have smooth crap. Fiber just ensures that you're going to have a "smooth" feeling and stuff don't get "forced" out.
If you're sitting down for 15 minutes, and crap is coming out smoothly, you're fine. Don't rush it, cause that too is just as harmful as sitting for 15 minutes and crapping hard.
Basically, if you have to push it out really hard, and rocking back and forth and feeling bloated, you should kick up the fiber intake. But if you're having smooth sailing for 15 minutes, just keep doing that.
You and your butthole got to stick together for life. If one dies, the other dies too. So don't force things out of it!