NopCommerce 2.80 Page Load and Product Search Optimization

I'm new to NopCommerce but took over a website in use. First page opening time and product search get too slow, sometime it gets 20 second to open the page. The server is well built with 4 cores and 10gb of ram. There is no huge data in database and categories not too much however somehow nopcommerce takes too much time to load it. Since previous developer edited too much on current system we can't upgrade from the version 2.80 to higger.

Please give your suggestions about the proper way to speed up NopCommerce 2.80?

Website: http://www.aktuelofis.com

See this topic

I've already seen this post. It doesnt give any solutoion other than changing slow hardware. However in my case the server is fast but nopcommerce is slow. What I need is some sofware optimization not hardware. Thanks.

Turn off javascript bundling this should help a bit.
Not sure if 2.8 version have these futures: Ignore ACL rules (sitewide):  and Ignore "limit per store" rules (sitewide):  if not used check these.
and see post https://www.nopcommerce.com/boards/t/23515/substantial-bottle-neck-in-nopcommerce-30-catalog-pages.aspx?p=3#96599 and

https://www.nopcommerce.com/boards/t/23325/performance-in-comparison.aspx you may have to apply changesets to the source code.