I use a Castle 10 Amp Voltage regulator set at 7.5 VDC for JP Retracts. Too much voltage can burn the Retract motors out. Also, there are current limiters in the LGC15. They have to be set to prevent the retract from burning out. The limiters shut off the power to the retract motors. This is why you should not try to power the retracts directly with a power source.
I just followed the book that came with the LGC15 and I did not have any problems. I also helped with several posts in this thread. I have several LGC15s, and I have gone through several other retract controllers, all of which did not work anywhere near as well as the LGC15. The only landing gear controller that really works well is the LGC 15. I just push the slider on the transmitter up fully and all my planes come to a smooth straight stop. The second one you get can use the same basic program with just minor adjustment. It take about a minute to swap the program with the Sd card. Well worth the effort to figure out the LGC 15's programming.
Read this entire thread. Then re-read the book. Set the retracts and controller up on the bench and figure out what the book is telling you. Then do the install. Also, I am not sure the current version of JP gear handles 2S lip. I do know they will handle 7.5 VDC. Do not try to power the retracts directly w/o a controller.