Sluggish playback of simple bezier curve animation in blender 2.79 and 2.8

Hi
I just reopened an old project of mine with a simple beziercurve camera animation. it runs fairly smooth in blender 2.73 (~10fps) but totally sluggish (0.2fps) in the latest blenders. but when viewing the scene in the latest blenders it renders smooth inside the viewport.

any ideas what could be the cause? tunnel2.blend.zip (258.7 KB)

cheers

martin