I run 17" wheels right now and TEIN flex will lower the car right on top of the tires if you want. I think the specs you read on them are wrong for the Supra. When I first put them on I adjusted them about 10 turns higher than the lowest setting and when I took the car off the jack it actually DID sit wheel well ON the rubber. Had to re-adjust to raise it up. Then when I got on track, diving into a 10 degree banked turn under heavy breaking it would rub on the top of the wheel wells so raised it up 4 more turns. Still got a brief rub.
I could go a little lower in back but I will probably go 18" and a little wider back there so I'll wait and see how that works.