You're correct. Look Keos do not have a flat 15 mm attachment. They come off with an 8 mm hex on the inside of the crankarm.
A hex key will not give you enough leverage to take them off. You'll need a socket and a long handle. A breaker bar will give you more leverage, a flex head or universal joint will give you better angles to maneuver around the frame. If they're on good and tight, don't be shy about asking someone else to hold the opposite crankarm so you can use both hands on the breaker. I know I can't do it by myself, and I consider myself pretty strong. It's just awkward to do it by yourself, since you have to reach through the frame and exert a considerable amount of force... and the opposite crankarm is as long as it is, and you can't make it longer to get more leverage on that side. If you cheat

and use a pneumatic driver, make sure you cushion your hold on the opposite crankarm with a folded shop rag or something.
The other
very important thing to remember is that since you're going in from the opposite side, you're actually pushing THROUGH the crankarm to remove the pedal, in the direction that would ordinarily be "tightening" for the respective thread orientation. So as you look at the Allen head on the inside of the crankarm, looking through the frame, you're going to turn the right pedal spindle clockwise to remove it, and the left pedal counterclockwise.
Park is pretty much THE brand when it comes to bike-specific tools, but when you're talking about "regular" tools like sockets, screwdrivers and hex drivers, Craftsman tools are a lot more easily available, pretty economical, and guaranteed for life (e.g. when you round off a driver or let your feeler gauges rust

all you have to do is bring it back to Sears for a free replacement, no questions no receipt needed). Not made in the USA any more though.

And I'm not familiar with Park's whole line, but it may be that they don't make some "regular" tools that are very handy for working on bikes (like the ball-head long Allen socket I used to take off my brake levers the other day).
HTH.