I'm stuck on lvl 15 too. I almost passed it once but the last coustemer took their money and ran so I didn't get the goal. Help please.

I can try to give you some tips, although I'm sure you've read them all before but you never know!

1. ALWAYS color match. The way I did this is reserve the front row for all your color matching. For example...put all your red cars in the front left spot (and them move them to the back in order of longest wait time), park all the blue cars in the front middle, and them move them to the back) I'm sure you all have noticed by now that a square only matches colors with the car on the first park.

2. Moving cars is a god thing. I'm always rearranging making room for more cars. I always try to fit in as many cars as possible at a time (of course leaving one spot open or else they're all stuck!)

3. Park the most impatient customers first whenever possible i.e. the cell phone guys, limo drivers and business women. The young girls and even the SUV guys can wait a round if necessary 

Hope this helps and if I have time later tonight I'll replay 15 and give you some more specific tips. I got an expert core on this level of 12,960 so it's definitely possible. Don't give up!!

Thanks for the tips. They helped. I was finally able to pass it.

Just bought the game in a store downtown, and I'm in the same level also. Hope the tips help.
 
.Isaiah.