With a lot of listings online, listing page becomes terribly slow

Hi,

For our purposes the Car dealer theme with all it’s features is awesome, however one thing is a real problem at the moment, that’s the speed of the listings page, see https://goo.gl/vrSnMI

Does someone has an idea how to increase the site? (it isn’t due to some plugins, I have deactivated them all to check it). Thanks in advance!