Simply highlight some tabs and clear out the RAM, occupied by the others
Press the ChRAM browser-action button in the top-right corner. You will be notified that the Random-Access Memory(RAM), occupied by the Chrome's tabs was cleared out - loaded data, like images, videos, text, page structures were removed from the RAM, while your sessions with cookies for the visited web-sites are kept.
If you highlight(Ctrl+Click to select) tabs from various windows of Chrome, they will remain in the same state, as they were, before you hit that button.
ONE MORE THING: For your convenience ShortCut 'Alt+PageUp' will take you to the previous Chrome window & 'Alt+PageDown' will take you to the next one. If not, try assigning them at chrome://extensions. You can also disable them there too.