I'm not a SD/HD expert by any means, but for $1500 (as stated in the OP), I'd be looking for:
- a used Rem 870 or Mossberg;
- a few goodies & mods (stock, mag extension, sights); and
- the rest in ammunition.
Personally, I'm an 870 guy, but there's nothing wrong with Mossberg, either. IMHO, getting a basic gun and lots of trigger time is probably a better plan than a really fancy gun but no bullet budget.