As a starting point, you can check Mac2Sell, eBay (including completed sales), or Amazon for prices of similar models, to get an idea of what a reasonable price may be. Then adjust the price to account for condition, configuration, remaining AppleCare coverage (if any), etc.
Ebay is still showing most sales in the $1200 range, but I don't think they have the RAM and 2TB drive. I still think $1500 is too much (2011 3.4 i7 is usually around $1750 when it pops up on the refurb site).
Maybe try $1300-$1400? As many will tell you, post it for what you want and see if you get any interested takers. If you don't get anyone in two weeks, probably need to lower the price.