Sorry in advance for the length. My son is currently rolling 14 pounds.  In season he does regular saturday league and travel league. He also does a tournament most Sundays. He is a lower rev rate bowler (200-225). Speed in the 14s.  He has been bowling for not quite 2 and a half years (he will be 14 this summer).  He has gone from beginner to his current 174 average. He recently qualified third in his district for Pepsi States in U15 (okay...that part is bragging).

I have been fairly conservative in moving him up in ball weight.  There are many kids I see at his age, even younger, already throwing 15.  To each their own.  I don't think his move up is imminent and any decision will be made in conjunction with his driller (Lee at BowlerX) and his coach (Lee's wife).

That said, as I am wont to do, I look for opportunities to pick up future pieces if deals present themselves.  So I have started to keep my eyes open for some 15 pounders for when he moves up and I'm trying to be more thoughtful about selection (not just balls that he's attracted to).  He's into Motiv, so that is what I am focusing on.  To start with, I already have two:

Radical Guru Mighty (I bought it for myself, but he wants to try one at next level, so he bought it off me)
Motiv Sigma Sting: This is his benchmark ball. he has one at 14 and it is great in this regard for him.

What to consider from here?  He bowls on all range of conditions through the year.  THS (some lighter, some heavier), Challenge patterns of all lengths.

Current 14# arsenal:
Raptor Talon (he likes)
Primal Rage (he likes)
Octane (meh)
Sigma Sting (he likes)
Tribal (he likes...usually)
QZ2 (meh)

An earlier rolling heavy oil solid would be nice, and I'm unlikely to find another Talon.  Actually hoping the next Motiv release is a Talon replacement.  Something for short patterns? Broken down lanes?  Another Rage would still fit?

(Before I get these responses, yes I am, and will be, consulting with Lee and his wife, but I really would like to get some additional viewpoints, especially from Motiv type people)

Sorry for the book:

As stated above, the Forza seems to be the logical choice for the early/strong ball.  The Tag could be a replacement for the Tribal/QZ2 (assuming it is not the Backdraft). 

That would give him a well rounded arsenal that will be adequate for most conditions he faces.  I usually don't get equipment based on market success, but instead of what seems to be lacking in my arsenal.  If I go to a tournament and it seems like I have a gap somewhere, that is what I look to fill.

What would be difficult to predict is how successful he would be on the extremes with this equipment.  Shorter patterns (sport) are typically heavier in volume.  A lot of people feel you need plastic/urethane or simply the weakest ball in your bag to attack these patterns.  Truth is, you can use stronger stuff assuming you know how to set up your equipment along with the ability to control your breakpoint.

Heavier patterns a lot of time don't need the strongest piece in the bag if you can play straight enough.  Once again, controlling the breakpoint is important along with not going away from the pocket too much, especially with lower revs.  I have seen many people be successful with roughed up Rages on long patterns. 

As far as additional pieces, it would depend on how successful he is with what he has.  The Venom Shock is a great piece for a lot of people especially on sport shots.  The Apex has been hit or miss with a lot of people depending on the surface prep they have.  The Octane has been a bust in most people's eyes along with the Tribal Fire, though not as much as the Octane.

The Revolt balls (Revolt and Revolt Vengeance) have been very successful for heavier volumes, especially the Revolt.  It would probably fall somewhere in between the Forza and Primal Rage, but closer to the Forza.  The Revolt Vengeance was suppose to be a Sting replacement of sorts.  It is a great ball, but not sure if it will reach Sting level of success.

Lastly, considering the purchase of equipment in 15 for future use.  I am not sure how much I would devote to this.  When I was a kid, I didn't want the ball from 2 years ago, I wanted the new one.  Not saying the old ball will always be better (Sigma Tour), but to a kid it is different.  If it is a ball he already has and he loves it along with be a market success, like the Sting or Rage, then I wouldn't balk at it.  But don't be surprised if he isn't as enamored by a Revolt in 2 years.

7 balls and 174.  I think there is a larger issue here besides ball weight and "arsenal" choice.

  There is some truth in that, but that issue is mine.  I did mention he only started less two and a half years ago and is 13 right?  Two years ago today he was 120. last year today he was 156.  Over the last month and a half he is 184.

Yes, I could hand him one ball and tell him he needs to make it work on a THS, Atlanta, Los Angeles, Tokyo, Women's US Open, Seoul, Montreal, Athens, etc.  But I think he's better served with having the ability to match up when he goes to tournaments.

For me, there would be no reason to have multiple balls.  For him, there is a reason.  And he uses them.  When he doesn't, they get sold.  Oh, and he pays for them with money he saved. Plus the fact that he's already won about 3000 in scholarship indicates to me that it's not a bad problem.

What is his ball speed, rev rate, etc?  I know he's into Motiv, but if an early rolling solid is a desired ball, the IQ Tour by Storm is PHENOMENAL!! When he does move up to 15lbs. his ball speed is likely to go down a bit which you may want to factor in to the ball choice.