That may do it, then. Generally, lumen’s best use cases are for modular or destructible worlds and dynamic TOD. If your interior won’t be subject to any TOD, you may be better off just baking it. By your high setting I’m assuming you’re shooting for 60 FPS?
And I would just try a rect light if you can afford it. It can be explicitly sampled, so way less artifacting, and it will scale down better.
If you want to avoid light-leaking, extrude your planes and add some thickness, or put ‘blocker’ geometry around them.
The issue is that lumen is a project-wide setting and you have to live with the results you have in all scenarios. With the look of your outdoor, seemingly open-ish world, lumen can solve that very well. But detailed interior lighting may be more challenging.
What’s your lumen scene visualization for the exterior?