18 months is nothing. LH took LX over more than 10 years ago and their IT systems still can't even say boo to each other. Bookings not visible from one side to another. Checkin may work, but more often than not you have to flip from one to the other. APIS information getting lost from one to the other. In other words, the merger is largely a marketing thing, a lot of hot air.
As it happens, I find IB not that bad. Their long-haul product in J is very pleasant. The 330/340 J cabin doesn't have the dormitory feel of the 777 and the 2-2-2 layout ensures that most seats have aisle access. Sure it's Spanish, but then BA is er, well, British. Short-haul J is similar to short-haul J in BA, not much difference frankly. Seats in short-haul Y are pretty awful, but frankly I prefer the BoB catering in IB Y to the rubbish served on BA short-haul Y.