Wire length/gauge danger?
Also, if you go to 180 watts of load (15 amps) this is more of a load than 16 guage can safely handle. #14 house wire is only good for 15 amps & you are thinking of putting a possible 15 amp load on a smaller wire.
Just because it is low voltage, don't be lulled into thinking it can't pose a safety hazard.
What do you mean by:
"......by just connecting all into one circuit." ?
You can do this safely by having multiple branches from the same transformer......(were all the old transformers mounted in the same location?)
The problem occurs when you try to put all the fixtures on a single run............
Where are you coming from? The load is 180 watts. Watts/voltage = amps
My calculation shows 1.5 amps. Just hook it up and try it. You may have voltage drop and the last couple lights dimmer, but then again you may not.
The voltage is 12. Thus 180w / 12v = 15 amps. This would be the total load on the x-fmer and the wire at the beginning of the run. Unless all of the lights are at the end of this long run, the load on the wire at the end of the run will not be 15 amps.
As previously stated, I believe that #16 wire is too small from a safety standpoint .