Yep, it was a very poor decision.
I could understand if it went for the character being like 12 to 50 maybe, but an actor that is 22, changing to an actor that is 30 is stupid.
Ser Laenor's new actor barely looked any older than the last one!
As you say, no attempt has been made age Daemon or Christen so the whole thing just looks weird on screen.
This isnt going to be the only time jump AFAIK and the current character was cast first and clearly she couldnt pull off a 15 year girl look but could be made to age to 50.