An AR-15 that started as a unassembled Title I lower, which has never had a stock, doesn't need to have a barrel over 16" and 26" overall length... It's not a rifle.
The firearm described by the OP is a pistol under Federal law, again, assuming it was made from an unassembled lower. The problem is, in MA, it needs to be AWB compliant.
If someone where to take an AR-15 lower that's a rifle, and remove the stock, that's fine, but now the Rifle requirements come into play, as that lower it's self is a rifle with or without a stock. It must have a barrel over 16" and an overall length over 26", or if shorter, be registered as an SBR.
Nope... Not an AOW. It's not a combo gun with barrels under 18". It's not a smooth bore pistol. It's not a covert/gadget gun.
--EasyD