Sounds like you've just answered your own question. You should probably get
a 19. I have a P14, which I love and have owned for 29 years. But I sail
mostly singlehanded. If you are planning overnighting or extended vacations
with your family, you will probably find the 15 too small. Even for
daysailing, three is a crowd on a 15 if conditions are lively, but okay on
a quiet day, IMHO.
I may get a 19, with the hope that my wife and other family members will
sail with me more, but I'm put off by the greater complexity, more
expensive maintenance, and the need for a heavier, more powerful vehicle to
tow the 19.
Harry Gordon
P14 #234, Manatee
Mountain View, CA