Thank you for your answer. I started from scratch once again, one mod after the other, ordering them by type and I am now at a third of what MODs I used to have and same problem everywhere, frezzes in Whiterun, Windhelm.... but not related to dialogue; so my first analysis was wrong. Any enclosed space (city, building) can freeze but it's not systematic, sometime i can walk in windhelm and freeze entering the temple, other time I freeze entering windhelm.... As if something was building up and froze everything, some kind of overload.... This time I don't have 4 K textures everywhere, have limited parallax meshes which I also suspected, just the main mods (LotD and all dependecies, many DLC sized MODS, Cities and towns overhauls) without the hundred patches for the moment I'm about to leave Skyrim for good, been playing since it was out with LE, never stopped and never had this type of problem. Must be my load order, surely is because not everyone has this issue.