Replacing old salt cell

We purchased our new house a little over a year ago and inherited the system we are currently using. I am new to pools, but the first year went fairly smooth. We estimated our pool size to be approximately 12,500 gal, we use a sand filter and have a salt water system. I recently brought my salt cell in to be inspected, and it failed inspection. The date on it was from 2006, so it appears to be time to replace. Right now, we have the Aqua-Rite t-15 salt cell. I did some shopping online and noticed this cell is used for 40k gal pools. Therefore, I was thinking about downsizing it to a lower capacity like the t-5 (for 25k gal) or even the t-3 (for 15k gal). My question is, should I stick with the t-15 cell as I had before, or can I lower it to something more fitting the size pool we have?

Thanks,
Mike