Pond is near a stream/creek I did do a test dig with backhoe and hit water at about 6 feet. How to I accomplish a 12-15 ft deep and keep water in the pond?

You have 2, maybe 3 basic choices:

1) Pump water out as you construct it. Fight the water the whole time and pray that you find enough clay to line the pond, praying that you can get it dry enough to compact the clay around the whole basin and seal it.
2) Pump the water out as you construct it. Fight the water the whole time, getting it constructed like you envision. Stop pumping and let it fill from the ground water. Pray that your groundwater level stays high and put up with fluctuating water levels in the pond according to the groundwater levels.
3) Dig the pond as in #2 above. Sink a well to keep the pond full. When the ground water levels drop and you have to pump water to keep it full, contact teehjaeh57 here on the forum for his polymer pond sealant and apply that to the pond, then pump it full of water and add water as required to keep it full.

Were you planning on a groundwater pond, or a pond supplied by surface runoff?

Are there other locations on your property for a pond?

esshup, has described the fight you will have in the current location.

Can you move up the slope of your property? If you find wet clay at a depth of 15-16' at a location up the slope, that would probably be a good location for a pond 12-15' deep. (Assuming that location has the correct watershed and drainage to fill the designed pond.)

How does catfish paylakes keep water in their fishing holes?

Not sure but I remember one that didn’t.

Buy an old dragline, don't worry about the water just dig, just hope you don't dig through the clay. The bigger question is what are you going to do with all the dirt your digging out? Where are you going to put it, how far do you have to move it, etc.