This option was introduced as a method of gaining those options in a method outside of styles (i.e. learn one maneuver for a single style or for many styles).
Yes, it is quite possible that the costs are too low and need to be adjusted , but that actually depends upon the campaign setting and how easy or difficult the GM makes it to learn (i.e. the costs are likely fine if you have to find a teacher to learn the maneuver, as that creates and extra onus, and in-game one, that can be used to great effect - only Master Cho knows the death touch strike, and nobody has seen him since he went in search of the Crystal Caverns of Croomash, so to learn that move, you must first find Master Cho)
Also, given that an average character will only have 35-40 DPs per level, 15 points is more than one third of that, and that is points taken from other skills (and only one maneuver is allowed per level).
Now, if you are using RMFRP, (which was not taken into account in the EA#8 article), you should likely triple those costs.