Several things:
1. Ok, 15w or 11w - not a big deal, the difference in energy savings less than 10%. Irrelevant worry.
2. But real issue is spectral content of light, it is not same, and frankly, I find flourescent light very unpleasant.
Protip: if you absolutely cannot live without the incandescent look, get the bulbs you want at a photography store and put a dimmer into the power line (because they're typically 200w+). You might get some sticker shock with your next electricity bill, though.
I'm not affiliated with Viva-Lite, just a happy user. Having 26W model here, it's maybe bit cold (5500 K), but still reproduces colors accurately.
edit: At least my lamp has quite long warm-up time. I haven't actually measured it, but I think its far longer than 10 minutes used in the article. Thats a major downside in ESL.
edit2: I actually forgot to add the link: http://www.viva-lite.com/