Well I just rehomed my Silver which is 14" and was in a 75 gallon tank. I've had him one year and one week, when I got him he was 3-3.5 inches. He could've stayed in that 75 for a little longer if needed, up to 16".
I beleive the growth rate for my aro was a little slow though 11" in 12 months. I have heard of aros growing as much as 2" a month but I don't know if this was steady for any length of time. But you could have a 16" aro in as little as 7 months if ya start at 2" I guess.
So, I would say at best you would have one year. In 9 months you better have the other tank in sight though.
Also I do feed my aro live fish, they are convict cichlids that I breed. I would stay away from live foods. They are not very healthy and have a high possiblity of disease.