This sells for maybe $2100 new in stores,
so at $1500 you're getting a discount, but
not a big enough one for a used digital piano,
in my opinion. A digital piano is essentially
a computer with a keyboard and speakers,
and so they are strongly influenced by
pc pricing. For example, if you buy
a pc for $2100 new, as soon as you walk
out of the store with it it takes a
steep drop in price, and you could not
sell it used for $1500 even just a day later.
A month later you might be able to get
$1000 for it if someone is generous. A
yr. later you'd have a hard time getting
$500 for it.
Digital pianos follow this type of pc
pricing to a large extent. A ten yr. old
digital, like a 10 y.o. pc, is worth little,
maybe a couple of hundred at most, even
though its performance will be similar to
brand new pc's. I bought a digital console
in 1989, and it's still in perfect condition
and performs similarly to brand new ones,
but like a 1980's vintage pc it's essentially
worthless.
Thus, in my view, $1500 is way too much for
this, even if its performance is identical
to a new one. Moreover, if might be a
yr. of more old and out of factory warranty.
The absolute maximum you should pay
for something like this in my opinion is
about $1000, and that's being very generous
to the seller. I personally wouldn't pay
more than about $500 for it even if it's
in perfect, new-like condition.