I can only compare it to my current Fiesta ST.
However, the Cruze should be under the same regulations.
They're made to be compatible with E15. On my Fiesta ST, there's a note "No fueling E20-85".
Strange. I probably could fuel diesel, or E100 and get away with it, 'legally' that is, because the sticker didn't mention not fueling anything above E85 nor diesel.
My experience with E fuels indicates that my ST is running better on a blend of 50% regular 87 octane, and 50% E15; resulting in ~E10-E12, with a 88 octane rating.
Anything higher (pure E15, E30,..) runs less efficient (lower MPG) and less power.
The hotter your engine runs, and the more knock it has, the higher you can tune your Ethanol levels.
If your engine runs very cool, on the stock turbo, there's no reason to believe it actually has more power on E15 or above, than below.
In fact, more than likely, the higher you go on ethanol levels, the lower your performance.
Unless you compensate by higher exterior temperatures, higher compression ratios, higher boost, or higher back pressure.
I think the only cars that benefit from E15 would be the 1st gen 2012+ models that are made to support E15 fuels, as they run considerably hotter than the Gen 2 models.
The 2011 Cruze (and especially the Eco models) don't have the proper fueling system to deal with higher ethanol fuels, and you probably could get away with E12 for a while.
But 93 octane is still a bit better.
I wouldn't do E15 in them, as they are made for E10 fuels and no more.
Running too much E85 in your fuel, and your car will run lean.
Some people on the Fiesta forum (especially those tuning their cars) have ran into piston problems due to lean burn, due to running too high ethanol levels (E50 and up).
If you had a dyno, you could do tests with what works best on your car.
But for my Fiesta, the butt dyno tells me the car accelerates best at 50% 87 octane, with 50% E15 fuel in a tank.
If your Cruze runs hotter, that ratio might be different.
You'd have to experiment.
And if you notice where the power starts to decrease (eg: E30 or E40), half that number, and that's roughly where your sweet spot is.
Eg: E40 starts accelerating slow, E20 is your sweet spot. Then try testing out E15 with E15+1 gal of E85.
I seriously wouldn't go over E20.