$1500 is not a small amount, you wouldn't want to spend on a used DSLR+lens and regret later ... besdies you say that your "T1i is probably going to die soon" due to it's current shutter count ... the same thing could also happen to a used 5D MK II ... of course if you absolutely cannot wait to get a FF DLSR, at this point of time for under $1500 your only option in my opion is a used 5D MK II & a used 24-105 at best.
But if you can wait, your best bet would be to save up $2000 by the year end (when good deals show up) and buy a brand new 6D + lens ... if you are lucky you might even get it for less.
Have you searched any of the stores to see which camera+lens come under $1500 ... I think that would help you narrow your choices.
Used is technically what I'm going for, I mean Canon 5dmkII are discontinued so new ones will become more expensive as time goes on if I'm not mistaken. I don't mind having a used body as long as I know the body has been taken care of I'll be fine with it.
And about that whole shutter count thing, I wasn't being serious haha. I'm just using it as an excuse to upgrade
Speaking from experiance of buying many lenses, speedlites and accessories that I was not happy with (later on), because I didn't have enough dough & patience to buy the better ones, has actually cost me more money than waiting & saving up to buy some good gear ... I'm a saggitarius (read that as: impulsive buyer), I bought and sold 12 lenses, 5 speedlites & countless unused accessories in the last 6 years ... if I was a little more patient, I would have saved quite a bit of money and got good gear that I did not regret later. Now that you have disclosed your dark secret about the shutter count
IMHO, if you really want to buy full frame, I think you would be better off waiting until you have at least $2000 and buy good camera & lens (I think sometime this year, you should be able to get brand new 6D+24-105 with warranty for $2000) ... you just need to keep an eye on sales/rebates that show up several times a year.
5D MK III, 16-35/2.8 L II, 24-70/2.8 VC, 24-105/4 L IS, 70-200/2.8 L IS II, 100/2.8 L IS, 40/2.8, 50/1.4, 85/1.8, 150-500 OS, 600EX-RTx2, ST-E3-RT, Rokinon 24/3.5 T-S, D7100+18-300 VR, YN568EX, 055CXPRO4+468MGRC2, 190CXPRO4+322RC2, Gorillapod Focus+496RC2, CamRanger, B+W filters, Konova K3/31.5 etc