MBP 15" mid 2015 + Aikitio thunder 2 internal monitor lag problem HELP!!!

[SimoLoveApple]

Hi all, I have a macbook pro 15 inch retina mid-2015.
I joined a Aikitio thunder2 with a graphics card GTX 1070 but there are problems with the internal monitor of my macbook.
first of all we will list the specific to this topic.
my macbook is equipped with two graphics cards, an integrated and a dedicated, integrated is an intel iris pro graphics while one dedicated is an amd radeon r9 m370x 2 GB gddr5, and obviously the eGPU GTX 1070.
the problem is that with the external monitor connected via hdmi to egpu doesn't show any problem while using the internal monitor that should take the video signal from the thunderbolt has lagged.
Mafia 3 with settings on external monitor turn 54 fps while on internal monitor turn 9 fps!!!
There is not much difference and it occurs to me that the problem is the thunderbolt.
members of tech inferno please help me!