Most of your yearly 15 tons is emitted via specific exhaust pipes, where capture part is quite easy problem, even without these cooling towers. The big problem is what to do with all of it: there is no commercial use/market, especially if you want that to be climate friendly, ie not dumped to atmosphere quite soon anyway. We'd need to think of it as toxic waste, similar to nuclear one, to be stored forever underground, but can we (as civilization) afford it?