I preferred using the transformer with the maximum 15-volt tap.
I had calculated about a 5.6 volt drop for that run with the LEDs so starting at 15 volts, I would have been borderline by calculation. Of course, the actual voltage drop may have been somewhat different after wiring up everything. Who knows? But I didn't want to be wrong after installing a lot of wire. And yes I considered the possible over-volting of the the LEDs. After a couple sleepless nights, I came up with the idea to combine cable sizes to control the voltage drop. Like I said, the drop was so borderline that even resistance from the number of connections could affect it. We'll see what happens when I do the project.
Starry Night Lighting
"Always look on the bright side of life."