Achieving 15 pt, is it worth it?

[Cyclopsided]

Power throw requires 13 Throwing WPF per level.
If you don't have have the WPF you don't get the damage benefit of PT. Keep in mind armor lowers WPF.

[Panoply]

I haven't tested this extensively, but from what I can tell, even if you don't meet the WPF requirements from your PT, you actually DO benefit from the extra PT. If you do not meet the WPF requirement, you cannot pick up ammo you've thrown, but you still do the extra damage from the PT above and beyond what you have the WPF for.

I've only tested it for PTs 4 - 6 with heavy throwing axes with a friend in the duel server. The only thing I varied was the PT, not the WPF nor the equipment of either two players, and I was at the WPF threshold required for 4 PT with the equipment I wore. I did enough trials of body shots that I can be reasonably confident that there was a significant difference in damage.

I could still be wrong, and it's possible the latest couple of patches fixed the issue. I'm sure it's not intended though.

[Leesin]

I thought you did get the extra damage from the PT but if you didn't meet the requirements you suffered from less accuracy and maybe throwing speed? my 11pt @ level 30 with stones seemed to work fine and do alot of damage even though I had suffered with not enough WPF for the 11 pt message.

[Shik]

If you do not meet the WPF requirement, you cannot pick up ammo you've thrown

The reason why you cannot pick up the ammo is because you no longer have enough power throw to pick it up, meaning that you lose the damage bonus.