My build runs really slowly, like 25fps, in the editor it runs around 50 or 60 fps. Is there any obvious reason for this?
Are your graphics quality the same in editor and build ?
Yes, I can select quality from within game, lowering it and the res speeds it up but looks poor.
Unless you maximize your editor game view to fill the whole screen while playing in editor, you are running the game at notable lower resolution in editor. This makes a huge difference in performance.
Good thinking, but actually its more or less fullscreen in my editor (just windows task bar and unitys top menu). In the past when I made builds (before HDRP) they ran around 40% faster.
It is quite difficult to tell without look at profiling. You can check with Unity Profile and RenderDoc to find out what increased between Editor and Build.
It can happen if your build use integrated gpu instead of normal one.
Screen resolution is very important
Check that it is the same in both