I agree.  Ill be utterly shameless here and point you toward a mod I made that does some of what youre getting at, they dont get up to 15000 but they all start with around 5000 health and are much more capable than the original cap ships.  (Btw its for Entrenchment 1.02 so youll have to be playing that to use the mod).  I'd love to see regular sins like this but I doubt such a change will happen.  Heres the link to the mod if you so wish to download it:

http://www.mediafire.com/download.php?w2imghnymgn

Capital ships are pretty tough as is.  The issues I have with their longevity have more to do with the units killing them - nanos and assailants or huge swarms of bombers being the most likely culprits. 

In my mod, squads are slightly weaker, with increased dmg but less ships per squad.

Caps are much stronger, first battleship maxes out around 12k hull, (new) second battleship maxes out around 15k.

weapons for them starting around 50-60 and reaching 80-100.

to balance that like he noted above, a maxed out vasari starbase has 50k hull and 20k shields.

starbase weapons start around 80-100 and max around 200

all the prices were increased also, so Caps and Starbases are costly but worth it.

i have a "super carrier" Cap that costs 50000 cr before any cost decreasing research.

they also have higher fleet point counts

frigs and cruisers are slightly upgraded but not much. frigs pop like frigs should. and when squads come under heavy fire, they go down quickly. i also made it so all Caps but the siege have at least 1 wep that can attack squads.

i think it is quite balanced and is more rewarding. i also fully re-worked the experience system and, well, everything. you get the idea

Couldn't we just get a similar effect by lowering the effectiveness of regular weapons against capital ship armour types?  Really, we only need to look at LRF and strike craft.  Light frigates and heavy cruisers don't have the range to swarm around a capital ship effectively, and nothing else can seriously damage a cap anyways.

Bombers are the tricky case, because they scale too well, and if we nerf them for the late game we stand to make them worthless early and mid-game.  I think the solution here is a DPS cap.  If a capital ship takes more than a certain amount of damage within a 1 second interval, further damage is ignored.  So, if the DPS cap is 400 (for a 4000 hp capital ship, that's a 10 second lifespan, fairly reasonable considering they don't get much tougher than that) and a fleet of 100 bomber squadrons descends upon it, they will deal a mere 400 damage because their attacks were too synchronized.  This would mean to get full effects out of your bomber horde, you'd have to stagger your attack, giving more time for the capital ship's fleet to accommodate and attempt to survive.

  Na, you guys are simply trying to make things complicated that doesnt need to be complicated, the simple fix that i find works amazingly well is simple, make caps stronger, actually what i do is make everything stronger, personally i found the base stats for just about all the ships and caps were stupid low.

 My years of playing WOW has taught me one thing, nerfing is for ignorant people....end of discussion. If one aspect of the game is OP, then tweak everything else out in the game to be a little OP also, makes game play so much more fun.

 Don't be afraid of the firepower boys, embrace it like men, now stop crying like b!tches and blow some sh!t up, peace.

actually, i'd say that if you had a horde of bombers descend on something, they'd melt right through the debris. then again, not that that kind of attack leaves debress unless their hulls are made of dust.

Ok, so you melt the ship's outer armour.  There's still going to be a thick plume of super-heated plasma surrounding the target afterwards.  I think that will block just about any missile.

Considering the numbers I'm throwing around (400 DPS) you'd be hard pressed to achieve that kind of damage through any other method anyways.

if you guys are serious about modifying damage to only capitals, the answer is found in Gameplay.constants:

DamagePercentBonus:ANTIVERYHEAVY:CapitalShip 0.75 (for strike craft)

DamagePercentBonus:ANTIMEDIUM:CapitalShip 0.75 (for Lrm)