Hi, I think you have the same questions as myself and a lot of other Precision users - poor performance because everything is being forced to use integrated graphics.

I have posted about it here: Force DWM.exe & Windows processes to use discrete GPU? Precision 5560 SLOW & unresponsive - Dell Community

That includes a description of a partial workaround. I say partial because I haven't been able to find a fix to get the laptop to use the discrete NVidia GPU for everything on a permanent basis, but I have been able to get it to use the discrete GPU in specific windowed or productivity apps. If you're using fullscreen 3D apps, the laptop should already be using the discrete GPU for those and I think my thread mentions how you can check that in Task Manager by seeing which GPU the apps are accessing (GPU 0 is usually integrated, GPU 1 is usually discrete GPU).

With these laptops, there is no hardware switch between the integrated graphics and discrete GPU - even if you get the laptop to use the discrete GPU it has to funnel everything through the integrated graphics channel. This is especially the case with external monitors on this laptop because there is no direct connection from external monitor to discrete GPU - everything goes through the integrated graphics. That doesn't mean your programs and processes can't take advantage of the hardware power of your discrete GPU but it will be funneled through the integrated graphics channel and potentially bottlenecked by that. It's not great in all honesty and for the price of these laptops I really feel it's a terrible design choice by Dell not to have a hardware graphics switch.

Hope that helps a bit even though it's not a real fix. I've been banging my head against a wall with this for five months.