There were only 2 series of D15. Series II had 46 belt hp and the 160 cubic inch engine. We have one - great tractor. It could be had with a 3ph/drawbar combo but that is apparently quite rare - most seem to have come with snap coupler (separate drawbar and 3 point hitch - have to remove one to install the other. 5 minutes but a hassle if you switch regularly or have a back problem).
D15's in good shape sell for up to $4500 or more without implements. I haven't seen one sell for less than $3000+ yet, but you don't see too many for sale. The resale on D14's and D15's always surprises me. If the engine's just been rebuilt I'd say it's probably worth it if the sheet metal and the rest of the tractor's in good shape. You're not getting a bargain, but you're not getting "taken," either. Fair on both sides.