I checked this site, and Lubuntu Software Center but could not find any guide. I guess it has to be manually installed?
On a related note: will Chromium do better or as good as Chrome on Lubuntu 15.04 on a rather speedy Laptop (Intel i5, 8GB RAM)?
Chrome you install from here. Linux systems (not just Ubuntu) will not have Chrome in the package manager due to the license. It will use your software center to install Chrome.
Will Chromium do better or as good as Chrome on Lubuntu 15.04 (on a rather speedy Laptop (Intel i5, 8GB RAM)?
It will be the same. Chromium is the open source version of Chrome. There are some features removed from Chromium ("usage-tracking" is disabled in Chromium) but in regards to "speed" both are the same. Bottlenecks are your system and internet connection; not the browser performance.
An in-depth article can be found on howtogeek.
Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
sudo wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add - sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list' sudo apt-get update sudo apt-get install google-chrome-stable
Thanks to Rahul