I am already aware about the issue : NOPCOMMERCE IS TOO SLOW !
I am working more than 10 years with Nopcommerce. From my previous experiences, I am sharing few possible cause which may reduce speed of nopcommece.
Possible Cause:-
1. May be your Nopcommece website pools hit the memory limit, which on a shared hosting is usually between 300-500 MB with some shared hosting offering up to 800 MB. I need to know about your hosting details.
2. To install a new plugin- nopCommerce is being restarted after the plugin is installed. You can notice the memory goes from around 200 MB to up to 700MB and if you keep doing this you might end up with more than 1 GB.
As per statistics, each nopcommerce themes come with a least 10 plugins, that means clients will have their website restarted at least 10 times during the installation of the theme and then the probability that they will hit the memory limit is quite high.
3. May be you have upload many products to a single page.
4. Using HTTP expires header, using web garden .
Solutions:-
1. You can run your websites without any memory limits, you won't even notice that because once the Garbage Collector is triggered it will remove any unused memory and your website memory.
2. Need to use a dedicated application pool for each website.
3. I am suggesting you to use 32-Bit application pools.
4. Ensure that ASP debugging is disabled in IIS
5. Use static and dynamic compression.
Please Share website- need to check it before commitment.