If it aint broke don't fix it.
You like your shorter boards, stick with em (especially if they are handling 15ft surf

)
Honestly, I think if anyone is leaning toward getting new boards or trying something new. Look at the guys who are riding waves the way you want to ride em, take note of what they are riding and go and see the guy who made the bloody thing. Takes all the guess work out of it hey.
I'd be interested to know which guys you consider to be surfing awkwardly, I'd be willing to bet they aren't riding necessarily the ones riding the longest boards

If you don't like they way guys are riding these longer boards what would posess you to go out and order one?
There is a misconception that guys are going to these longer lengths purely to enhance paddle speed. I choose the length of my board in direct relation to the lines i want be able to follow on the wave face, plain and simple. Some guys ride their shorter boards to great effect, but personally I would feel like Mr Squiggle on anything less than 5"10" ( I'm 6' and 92kg).
There are probably 10-15 guys in the world that ride kneeboards the way I like to see them ridden. But I have no interest in converting others to my way of thinking( unlike alot of others in "kneeboard world"

) each to his own as they say

.