Hello,
I used to have an issue with Lumion 1 before that caused my render times to reach 25 Seconds, Back then I was still a "newbie" with the whole Real Time rendering stuff and I really noticed that most of my models were not optimized for such engines, for example a soccer field had no more than 500 polies yet the 2 Goals with their nets were over 350,000 Polies each !
I am revisiting and old project That I created with Lumion, as the first was a fast rough job to finish on deadline but now I have more time on my hands to smooth things out.
My PC setup is :
Intel Core i7 950 @ 3.07 GHZ
8.0 GB DDR3 Rams
ATi Radeon 6950 1GB DDR5

I've redone most of the model from scratch ... to suit Lumion. I've even seperated the buildings from the rest of the model thanks to the excellent (20+ layer plus feature of lumion 2)
the base model without the buildings is around 250,000 Polies 137K Verts as Lumion prefers it.

which without any props (people/cars/objects) or trees, only texutred in lumion renders a frame in 3.94 Seconds ! Which is very nice ! Lumion reads 193K not 137K but thats ok ...
Sadly after turning on all the props/trees the verts rise from 193k to 5652K !
I thought the trees were adding up, but apparently it was the props !(vechiles/people/objects) they add alone almost 3000K of verts !
render time for the base model + lumion props + trees doubled to 7.6 Seconds !

now turning on my props (goals/lights/other misc stuff.. ) jumps the verts from 5625K to 9000K
Render times goes up tp 9.2 Seconds.
sadly .. turning on the optimized buildings and everything else .. the verts jumped from 9000K to 16754K, Render times jumps to 12 Seconds.
Which is still super fine with me ! for a scene this complex ... my problem is after a few renders from almost the same view .. or after a couple of hours of work ..
Render times seems to escalate even for the same scene .. for example the same scene without adding anything .. after a few hours of moving stuff around or pllaying with the camera .. renders in about 30 seconds ...
A night version with lumion lights renders at first in 25 - 35 seconds per frame then jumps to 90 frame per second !
is there something wrong with my gfx card ? or is it something known in Lumion that after a few hours of GPU load, FPS beings to suffer ?
for example the same scene I rendered in 12 Seconds, Rendered in 32 Seconds before Restarting the Computer !
What am I doing wrong ?
and is 16000K Too much for Lumion or Too much for a scene like this :

Note: My gfx card is updated to latest Catalyst Drivers and every component of the PC is up to date.
Thanks.