I think it is vastly UP. Assuming rounding up, it is 6 quanta for a 2/2 creature. It is 53 quanta for a 10/10 creature, or 78 quanta for a 15/15 creature. It doesn't really help at all against devourers or discord, since it drops you to 0 quanta, which is exactly the worst situation to be in.
If you never use the ability, you have an extremely inefficient creature. If you do use it, you lost a card.
Parallel Universe is powerful with it, if you can get it to survive. Even if you are storing 16 quanta, it is only 4/4 which could easily be shockwaved.
It should maybe be +2/+2 per 5 mana with 16 and 24 for the maximums. Perhaps it should have a base of 0/3 to keep it from being killed by all PC. My hunch is that even with PU, it would not be overpowered. You are spending 9 mana and 2 cards to double your quanta. You need 24+9=33 mana to make it as efficient as nova. Imagine how bad nova would be if it you had to have 33 mana to cast it.