More Power

If you're running TMCC or Legacy exclusively why not hook the powerhouse direct to the track? A TPC isn't really needed.

Ron

You loco should run fine at 15.3v,however it sounds like you may have inadvertently lowered the voltage. You can check your TPC manual for instruction on page 11,to reset the track to full voltage address the TPC , then push AUX1,AUX2, then 0, you may also turn the red knob clockwise to restore full voltage. Check track voltage with a load on the transformer i.e. when the train is running for an accurate reading. Thats alot of "juice" going to the track, if your not already using it Lionel reccomends 14GA wire from the TPC to the track. Flickering lights is a signal issue not a voltage issue, could be a few different things possibly a "ground plane"issue or a problem with where the base is plugged in. Its recommended the base be plugged directly into a wall outlet, one side of the signal is transmitted via house ground wiring. "Ground plane" issues are usually caused by something metal interferering with the signal, i,e. tracks going over one another, chicken wire in a mountain etc. If your shelf layout is hung with metal braces this could be your problem. You can search "ground planes" for more info.

You should measure the voltage AT THE TRACK with the train running.  That reading will tell you if you have any voltage drops in the wiring.  If you use the voltmeter without the nominal current being drawn, you won't detect any bad connections.  You could have a nearly open circuit without the voltmeter registering any drop if there is no load!

Do you have a robust network of power feeders to multiple points on the layout?  What wire gauge?

If you are actually getting 15V to the rails, you should be able to operate properly.  Some fellows reduce the track voltage from 18 to 15V to minimize arcing due to derailments, and their trains run just fine.