Keep in mind that you will be recharging much less

There are ships which would benefit more from capacitor amount than recharge Ragnarok Online Zeny, specifically capital ships.

With the common method of killing a capital ship being the neutralization of their capacitor, more capacitor will literally slow down the enemy much longer than 2.6% faster peak regeneration. Also keep in mind that you will be recharging much less until you reach 33% capacitor for optimal recharge.

With the recent nerf to ECM, the new ECM rigs will keep an EW player ahead of his game. Since capacitor, power grid or weapons rigs are likely to be more useful on most setups, electronic warfare rigs are likely to be of very specialized, but effective use.

With the same amount of capacitor and 85% of the normal recharge time, in effect we end up with a capacitor per second generation increase of 17.6%. The 15% capacitor amount rig, however, would be calculated as 15% more capacitor and the normal recharge time.

So that rig actually does increase the capacitor per second generated by your ship by 15%. This means that the capacitor recharge rig is about 2.6% better than capacitor amount, but is it always better?

In effect, more capacitor gives any setup more resistance to Nosferatu and neutralizers as they reduce the percentage of your capacitor that can be stolen or destroyed per unit time. This may also make it ideal on Battleships in place of cap recharge rigs.