If it has 16gb, it's not a MacBook Air. The maximum is 8gb.
Also, you didn't say whether it's an 11" or 13" model. Sorry, I can't really help. I have a 2013 11" i7/8gb/512gb MacBook Air and still love it, will probably keep it until it dies. A few months ago, B&H Photo was blowing out their stock of 2015 11" i7/8gb/512gb MBAs for around $1000 brand new. This was an exceptional deal that a few forum members were able to grab. When they were available, Apple was offering 2015 refurbs of this configuration for about $1300.
The 11" MBA is harder to find in this configuration these days since it was discontinued. That might mean they sell at a premium to the 13" model, don't really know. Also consider the battery however. If it is still the original then you should budget for a new one as it may be nearing the end of its useful life. Last time I checked, Apple will replace the battery for around $130.