There are equalizers you can add to the sink side of the cable. If you get one, make sure it has its own power supply. The ones that draw their power from the 5V line of the HDMI cable don't work very well. For that matter, the ones with power supplies don't work very well, either. There is more to the problem than amplification/equalization can fix. And a lot of TVs employ equalization for high speed signals already.
FWIW you should be able to do 15m at 1080p60 with 24 bit color. Did you make sure DeepColor is turned off on the PS3? 36 bit DeepColor requires 50% more bandwidth than 24 bit.
If a good passive HDMI cable doesn't do the job for you, you are looking at using an active cable (Redmere based for instance) or some kind of extender product (like HDBaseT over Cat 6 cable).