Well, at least we figured out the problem!
There are a few things you can do from here.
First, since you seem interested in being able to have lights that can be turned on/off in your game, it should be noted that the lights are not the heavy part. It’s the shadows that are causing the problem. So, in theory, you could keep your lights, but just set a bunch of your objects to not cast shadows.
Another option is to lower shadow quality. Dynamic shadows are greatly affected by poly counts of the meshes that are casting the shadow. So, if you still wanted objects to be “casting shadows” but not be as high a cost, you could be a bit sneaky and get a bunch of low poly objects to set to invisible but leave “cast shadow” on in their details (I believe one of the settings of visibility/hidden in game still allows the object to cast shadow even if it is not visible at the time). Then make sure all your actual objects are not casting shadows, but put them in the same spot as the invisible low poly meshes.
And, the other most obvious, you can do what you have already mentioned and simply remove some of the dynamic lights altogether and replace with static.