It is important to keep in mind and to use the Exposure Control in the Camera Tab in the Render Dialog Box.
Consider these real-world photo examples. Notice that if the interior of the room is shot dark, that the exterior viewed through the window is exposed in such a way that the objects outside are understandable:
Notice that if the exposure of the camera is changed so that the room itself can be viewed in good lighting, the exterior becomes quickly overexposed:
In Subject: Master Bedroom
We can see in this great image by revered SketchUp artist and well-respected Twilight Render artist Tomyong that the external exposure doesn't match with what our eyes expect:
An attempt at correcting the exposure in post-pro was some-what successful, but it would be even better if the external exposure were done in the scene setup, eliminating need for much post-pro.
So, to increase the exposure on the exterior image:
Adjust exposure in the "Post-Process: Tone Mapping" area of the Render Dialog while rendering.
Set the background image you have inserted onto a backplate plane inside your SU model and set it to be a Light Emitter material template set to type:"fake" with power starting at 200watts/m2 (may vary depending on the scene and camera/tone map settings)
Example of real photo demonstrating interior vs exterior lighting with photographic exposure.