I understand that. But a fresh install with factory default settings should not have only 10-15 MB free memory. Because I have my own packages to install. eg: collectd statistics, some of my own maintenance scripts. From my previous experience, if memory drops too low, the router restarts.
And this is only due to the new admin panel. I know that it very useful than before but it is memory intensive. openWRT started using luci (which uses very lightweight lua language) to optimise their performance.