Iain Glen’s(Ser Jorah Mormont) thoughts on the shortened seasons appear to be that the GOT show runners wanted to go out with a bang. I call shenanigans!!!. I think there is no way they can wrap up the story they have told in 15 episodes and that they have every intention of turning it into a Trilogy of movies.
I suspected it when they tested the waters by releasing Season 4, episodes 9 & 10 in IMAX format and I’m more convinced then ever now. This series is the Lord of the Rings of the last 25 years. I’m sure the theatrical releases will do just fine.