After one of driver updates (or something else) got the same problem as you. Will use only Intel GMA if docked and using laptop display and external ones. If only externals - SketchUp will use nVidia Quadro with no problems. Even if I force to use Quadro in driver. No chance. So have to go “external monitors only” for big models. Strange bug. Possibly, Nvidia/Optimus/Intel are to blame. Or how SketchUp selects what graphics to use. 
Take a look at my post 7 or 8 in this thread. http://forums.sketchup.com/t/jagged-lines-on-brand-new-computer/19162/5
There’s a bit more info there by others too, hope it helps.
Shep
Agree, I have a gigabyte p34w v3 with GTX970, 14" screen 1920 x 1080 … light and powerful as I travel a lot, but at my office I have bought everyone Samsung 4k 42" TV’s and although we only have HDMI1.2 they seem to connect fine.
THe displays are brilliant as they equal an A1 drawing at 1:1
Sorry for “necroposting” - decided to write a small update in case if thill helps someone else.
Got mine Dell Precision m5510 (i7-6820HQ, 32GB RAM, 1TB NVMe, Quadro m1000m) and very happy with it, significantly faster compared to my previous m4700. And is almost twice as light.
Did you test big skp models with a lot of polygons with your Dell Precision m5510? Are you using AutoCad also in this machine?
The biggest model I worked on it was approx. 245MB. Worked OK.
Plus machine is driving HTC Vive with models up to 100MB, approximately. (40MB is more comfortable, but was surprised it was able to do it at all)
No, I don’t use AutoCAD. (only DWG True View)
I’m looking now for a new laptop, now I have an old MacBook Pro 2013, and if I need to explode big model from imported CAD model, it can take me 1 night to do it. I’m thinking now to buy Dell Precision 5520 or 7720 but I don’t know if it help me to solve my problem. By the way, can you check this model in your laptop?