I suspect you're right about the time taken with the final battle. The strong rumor during production was that Disney was refusing Abrams the additional six months he wanted, and it'd make sense if that ended up taking a toll on that sequence. I can see exactly what they were going for in both, and how it worked much better in the first: in previous Star Wars movies, the space battle sequences were largely unconnected with what happened on the ground. They were sort of like primitive video games, where you'd get to a very linear point where one story would unlock the next part of the other (taking down the shield, blowing up the droid platform, etc.) In TFA, he certainly set out to connect the two in both instances so that both are happening in the same sphere and impacting all characters continuously... you just get the feeling that it didn't quite work out as envisioned in the finale (also interesting to note the first one was where they had their IMAX camera which they didn't bother with for the finale!)