Can I use 88octane-15% ethanol in my 2011 ram hemi

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The owners manual probably says no. Most say 89 octane is the lowest. Look in manual if you have one or they are typically on-line. With that said, test your vehicle with that fuel. Next time it is very close to empty put 2-3 gallons in the tank and drive. If the octane is too low the engine will "spark knock" or "diesel" (a rattling sound from the engine upon acceleration caused by fuel pre-ignition/detonation). If that happens put an equal amount of premium fuel in the tank and the spark knock will go away. Short-term a spark knock won't damage an engine, but longer term can by causing over heating, vibrations, abnormal stresses ... hesitation on acceleration - poor mileage and poor engine performance. If you are able to use 88 octane-15%, without getting a spark knock, make sure you check your mileage and see if, or how much, it drops. Lower octane and higher ethanol both reduce mileage. What I always told my gas customers was to check your mileage with different octanes and see what octane gives the highest mileage (and then do the math and see if its cost effective). Say you use regular normally and you get 30 MPG. Then you try the mid-grade and get 33 MPG, so you try premium fuel but you still get 33 MPG. In that case the mid-grade is your best option, assuming that your 10% increase in mileage cost you less than a 10% increase in cost! But you do always stay away from fuel that causes a spark knock.
The rule of thumb is: The higher the octane the cooler the combustion, therefore the lower the octane the hotter the combustion. Higher ethanol means that the engine is running a little leaner and a little hotter.