Hello Jojii,
There are number of things you can do to optimize your project for better lighting. If you bring up your console command prompt by pressing the " `/~" key and enter command " profilegpu, " the editor will bring up a screen capture of all of your processes. This will profile where your memory is allocated and how much is being assigned to that process.
In this profile is a section dedicated to lighting. In that section you can see what specifically about your lights is taking up your GPU memory.
After profiling your GPU and finding where most of your processes with your lights are occurring please post again with the results. Also, you may want to switch your lighting to movable. Movable lights update every frame. This is a more accurate lighting calculation than that of a baked lighting which is built only once. Depending on your project size Dynamic lighting is less expensive than a large lightmass being drawn.
I am linking you to our documentation on lighting an environment. In this section it covers many lighting techniques and how they can be used in an efficient and optimized way.
I am also linking you to a lighting troubleshooting guide which covers common issues that you can run into when lighting.