It's almost impossible to get "too big" of a TV. I wouldn't sweat that.
At that pricepoint, you've got two options:
1) Go really big. Get a Mitsubishi DLP and you can get a 73" set. Can't vouch for Mitsubishi, but I had a Samsung DLP for awhile and enjoyed it immensely.
2) Go for quality. Pick up a 2009 plasma (probably a Panasonic). For $1500, you can get a 58" S1 series (which I upgraded to after my DLP; I feel it was a significant step up). If you want to go even higher quality, you can get smaller-sized Panny G10s or V10s, but I personally prefer a bit more screen size over the improvements offered by those sets. Others here will undoubtedly disagree.
Honestly, it depends on what you value; for the highest quality, get a Panasonic V10 series in the largest size you can for $1500 (I'd guess 50"). For the largest picture, get a giant Mitsubishi. I'd say the Panasonic G10 and S1s are choices in between that depend on what your viewing habits are.
My two cents.