After activating the theme, there’ll be suggested plugin listed at the top (if there aren’t, you can go to ‘Appearance > Install Plugins’ section as well ).
Try installing and activating these following plugins ( as it effects the importing process ). You can also install all suggested plugins at this step as well.
Follow the steps mentioned on the screen, then, you’ll get the site like the demo 🙂
You can add below code in function.php line 2 in themes/gecko/function.php and try import again. This problem of hosting limit memory. After import complete you can remove code.