what size tilemap is it and what is the size of the tilemap object you are making in the editor?
I have seen a few laggy things in the editor because I also have a fairly large project. One thing that helped me was to off-load all my function, variables other "global code" into #include sheets, this really helped my performance.
Also in setting I turn off things like, Animated UI etc..
EDIT: I just saw your GIF - that size looks like it should be fine.. although I can't tell the size of your actual tiles. I have a 3000x480 tile object (tiles are 32x32) and it runs totally fine (editing in the editor).