Put up a fraps of the whole of the final advanced level ( 18 ) ... HERE
Obviously don't watch it if you don't want it spoilt! It's by no means perfect and i die a few times through clumsiness. I just love that level so much though!
This was one of my favorite chambers too. I DLed and watched your vid, took a while to buffer it. It appeared when you entered the big room with the turrets the machine launching the orbs was not active and I don't recall seeing you activate the tram. I used totally different methods there and never had to jump through portals to knock over the turrets.
In the last room with the high ceiling and all the platforms it took me a while to figure out it had to be done all in one sequence but once I understood that I was able to get to the top with very few portals.
To those having mentioned how hard it is to do the challenges, yes and no. I thought all types of challenges were hard too after trying chamber 15's portal goal. Seems to me it said the goal was 23 at first then when I achieved that it now says 21. Can anyone confirm this?
I think what happens is they state the Bronze goal first then it drops to the number that represents Silver after completing that. My stats now say 23 Best, 21 Goal on Chamber 15 portal Challenge.
Anyway, it gets way easier than that on portal challenges if you find ways to circumvent some of the apparatuses. For instance after watching a Youtube vid, I saw one guy do chamber 15 with only 14 portals. He didn't even activate the tram or the lift and only one part was difficult with a long and perfectly placed portal shot he made. The trick is to shoot an opposite color portal while standing in the middle of the other portal.
The time and step challenges are no doubt going to be the more difficult but even those become more reachable when you factor in circumvention of apparatuses. Needless to say Portal hinges on how you place and use your portals. After seeing how you can bypass the machinery, I still tend to like the fact that you have to place your portals well and time things perfectly when you DO use all the elements of each map.
I really started to like how once you figure out how to get an orb to it's destined recepticle, you still often have be alert and hit the mark just right or set it up and try again. The challenges to some degree take that away by merely outsmarting the machines with clever portal usage, so it becomes less physical at that point.