I notice a small green puddle of fluid yesterday (felt slippery) close to the inside of the rear driver tire.
Got underneath to take a look but couldn't see much, just a green drop of fluid handing from
the bottom metal arm that hold the wheel on.

What fluids in the car are green? Anti-freeze, brake fluid, leaking shock?

I have a 2015 Cayman, 2 months old, 1,500 miles.
All gauges look good so far.

 

Green is coolant. You need to trace the leak back to the source. If it's too dirty to see where it's coming from, then wash off the car in that area to get rid of any dirt and existing fluids. Then see if anything starts to drip while it's sitting, and if not, start the car and see where it comes from. You can put the car up on jacks or jack stands so you can see underneath more easily. If you have a creeper this would be a great time to use it (wear safety goggles / glasses so it doesn't drip in your eyes). Make sure you have an extra support too, i.e. leave the jack or an extra jack stand under it if you use two jack stands to hold it up, or use at least two jacks.

Likely / possible sources in that area could be a coolant expansion tank or a coolant line. If all else fails, take it to the dealer since it's under warranty anyway.

 

Green is coolant. Seems like the car is pretty new. Take the car in as I am sure whatever the issue is would be covered under warranty.

-Luccia

 

It turned out to be a leaking rear shock - green fluid.
The coolant is Pink.