Power receivers are hard to build because it's very opinionated what OC's want out of them. As an OC, I personally only want WR's with a tad bit of strength/blocking (in the low 30's) for outside blocks, but that's about it. Breaking tackles as a power WR is all about YAC, but YAC is hard to come by once you get to Pro. I'd rather have a reliable WR who can create separation and catch first and foremost. Having said that, it IS possible, but in the current sim? Who knows...
http://goallineblitz.com/game/player_awards.pl?player_id=87163 (only Pro WR to win a gold pancake award)
Speedsters is the way most people go. Much safer and easier to build.
First off, you shouldn't be spending your 15 SP's, so glad you kept them. You're supposed to hold the points and train until you can soft-cap a single attribute in one big investment. This way you're not shooting yourself in the foot wasting training opportunities, since you want to train attributes when they're low to reap greater profits.
For now, train speed and get that 2/1 capped. Afterward, others recommend the straight-up approach, heading right into speed as the 3/1 cap, but to each his own.