Improve Largest Contentful Paint in mobile mode

I have just created a website www.marbellavistahomes.com and I have seen that the mobile version takes 12s to load according to Pagespeed Insights. Since I am new to this I do not know where to start to improve this. From what I can read from the analysis it is not mainly due to images but to Javascript scripts and CSS among other things. Do you have any tips on how to improve this without investing too much?

Thanks

This seems to be impacting the search placement of my sites. Anyone have tips on this?