Anything 15 seconds and under is pretty impressive. If you can get it down to 11-12 or even less, you are truly an amazing athlete. Even if you don't do parkour, this is a great skill to practice, as it is essentially a complete upper body workout, with a bit of legs thrown in the mix. This is also a precursor to the muscle up, so if you are able to do a good amount of these, you should be able to perform a muscle up without too much difficulty and vice versa.
Also, keep in mind that the time starts from the moment you make your first descent, and ends when your feet touch the top of the wall on the fifth climb up, not when you ascend back down. Have fun and be safe!