Welcome Giannis,
There is an exclude
parameter for most loop types. I imagine you could create some logic that checks for an already displayed post ID on the page and excludes it from the loop.
Perhaps you can create a list of post IDs that are already displayed on the page and then do a comparison within a post loop to exclude them.
I use this to exclude the currently displayed single post from a ‘More Posts’ feature:
<Loop type="post" count="3" orderby="date" order="desc" exclude="{Field id}">
<Field title />
</Loop>
Also, this reusable posts demo might be helpful in understanding how L&L can speed up your development:
With regards to performance, personally, I use Lightspeed cache (Advanced setting) and can achieve scores in the 90s on Google PageSpeed Test, but my sites are fairly simple with minimal plugins running.