I'd like to see a source on those tank-killing teams, if you're saying it takes 15 hits to destroy the tank.
If you're saying they do it by having 15 guys with RPG-7s and hoping that one of them gets the lucky hit, then I'd also like to see the source, because either way it would be interesting
Seriously though: I'm pretty sure it doesn't take 15 hits from RPG-7s to destroy a tank. From what I know, it takes one direct, full hit in the right spot and that's it.
However, with good armor, many hits don't deal much damage at all. Slat armor, for example can deflect RPGs (and bigger stuff!) ~50% of the time.
It doesn't take 15 hits to destroy a tank, but it may take 15 guys to get a hit. Some of your guys may not end up with LOS on the tank. Some of your guys may not end up in the side or rear arc of the tank, where there's a chance to kill it. Tanks don't operate alone, so having more guys to shoot at (other) tanks is also very helpful.
All these difficulties is why the west has spent so much money on making their anti-tank missiles smarter. If you are firing a Javelin at the tank, you don't really have to care whether you are facing the front of the tank. Since you have so much more range, you have many more opportunities to get LOS on the tank. You have a thermal sight, so you see right through smoke that the tank may throw out. The Javelin is self guided, so you don't have to worry about leading the target, keeping it in sight, or compensating for it's evasive maneuvers. Just shoot the Javelin and leave.
Now compare the cost:
An RPG-7 costs something like 2,000 USD and rounds for it are something like 500 USD a piece.
The 'sight' (Command Launch Unit) for a Javelin costs somethings like 150,000 USD and each Javelin missile costs something like 80,000 USD.