It's been a long time since I did any laptop gaming but you need to be plugged into power for the dedicated GPU to run I think. Aside from that I would check all the power settings for the system. Make sure it isn't in some eco mode or anything else silly.
I have a desktop with roughly equivalent hardware that I played RD2 on in 1440p and I was able to crank everything and still have 60+ fps consistently. Its been awhile so I forget the exact my numbers but I think in most areas I was able to stay over 100. It's really only the cities and other densely populated areas where my fps drop down a bit.
Edit: I forgot to ask if you have run any benchmarks in other games or if you have only tried RD2. At least that way you can determine if it's a red dead 2 issues or a system wide issue.