^^^ some people may not like the S model due to the less efficient heater and smaller backup camera/display screen but I really like mine. Personally I'd only want one with the QC/Charger package but it sounds like it has that.
There is some reassurance purchasing from someone you know, but on the flip side I guess if you ran into any major issues a few months down the line, how would that be handled. I guess the only real major issues I could think of would be the A/C bracket/hose if it hasn't been replaced under warranty(if it even effects 15's??) and maybe heater??. I haven't had any heater issues but I've read it can be expensive and I'm not sure again what particular models/years it would effect, I don't think it's very common. '15 should be under the 3 year full warranty for 6+ months more so thats good and would help with any of the issues I mentioned above.
Not sure if CC was added in '15 for the base S but if it's important to you, you should check it out. I believe rear seat heat was standard up through the '15 S models, but again verify if important.
$10.5K seems on the high side but the mileage is very low and I've more been looking at '13s and 14s so 15s are bound to be more, especially with the full warranty.
Does they have a L2 EVSE they'd include? If so thats worth a bit, if you planned on getting one anyway, that or a EVSEupgrade'd EVSE.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a