Correcting over-amped wiring... fire hazard?
If there are any problems, they'll appear at the terminations first.  

So as you work on that system, just keep an eye peeled for any thermal damage at terminations.  Discolored wire, melted insulation, arcing, anything like that.  

Truth be told, 14AWG wire is allowed for 20A - just look at the table formerly known as NEC 310.16... but this presumes 75C terminations (e.g. the receptacle will not scald your child's finger if he touches the outside while a wire is cooking away at 75C on a screw) and a bunch of other favorable factors.  So there is a statutory rule elsewhere in NEC that clamps 14AWG ampacity at 15.