Lightroom offers three ways to (automatically) set an import destination (I'm using Lightroom 2015.8 but I'm quite sure it worked like that before):

1. Normally Lightroom saves the destination folder if you chose 'into one folder'-Option at the 'destination' panel of the import dialog (you need to import a few pictures once though). The next time you open the import dialog your last chosen folder should be preselected (only works for copying and moving images!).
2. If this somehow doesn't work for you, you could define an import preset (https://helpx.adobe.com/lightroom/help/photo-video-import-options.html#import_using_presets). To do so, define everything from preview to destination folder (right panel) and save your settings as preset. Next time you want to import images just select the images on the left and chose your import preset. All settings, including destination, will be set liked you've defined them in your preset.
3. Last but not least, you could deactivate the auto import prompt (Edit/Preferences/General preferences - Option "Show Import Dialog When A Memory Card Is Detected") and manually import into your desired folder by right-clicking the destination folder in the library view and choosing option 'import into that folder'

(I'm not sure if the labels of the buttons are 100% correct since I'm not using Lightroom in English)