Well, if im right about it, the energy output from the reactors is tripled at lvl 15. So it could be worth it, but thats only if the formula used in the game works and the ones posted are correct

From my findings playing around with the formula, (assuming i did it right) the reactor values only change at energy tech level of 10X + 5, meaning 5, 15, 25, etc. I'm not far along enough to try it out but I like crunching numbers.