I think $4,300 is a fair enough offer based on all this info.
If you are really keen offer a little more.
I would hang tight for a couple of weeks and then call back to check in.
That is quite a price drop eh!
Wonder what precipitated it.
$15,000 was pretty steep and would be hard sell. $8,500 is more realistic.
Maybe the seller needs the cash right now!
If it is as nice as it looks it should be worth all the money being a 4 speed.
A bunch more photo's would help in the sale, plus more info like milage, specifics on work done, etc.