If your normal page time was at 8 seconds, you already had some problems to begin with. And without more information, including the scores your received there isn't much else to do but ask you a bunch of questions. So here we go...
- First are you using a CDN (content delivery network)? If not, you need to be.
- Second are you minifying all CSS & JS? You can do so through your CDN (Cloudflare is free), and I know w3 total cache does as well. Otherwise you could get another plugin to do so (but I wouldn't see the point of adding another plugin that 1 service and plugin do already together).
- What theme are you using?
- Are you setting expire header times? You can do this through your cache plugin as well
- Is your cache plugin setup correctly? (ex: Page cache, browser cache, opcode cache, object cache, ect)
- Are you scaling and smushing images?
- Are you lazy loading content (including fonts)?
- enabled gzip compression?
- How many plugins are you currently running?
- Are any plugins conflicting? (ex: doing same thing as other plugins or overloading requests)
- What settings do you have for Aliexpress? (ex: how much is updating and when?)
- When importing are you saving images to your server? (Saving them to your server lessens the request time from getting them from aliexpress, it also allows you to smush and optimize the images further to decrease load times).
Now if everything is optimized as far as that list goes (plus some I haven't mentioned due to this being off the top of my head) and you're getting pagespeed scores of 'A' and yslow score of 'C' or better, then most likely it is a problem with your hosting package or server configuration. In most cases its the cause of using the cheapest (slowest) hosting plan (i.e. shared). Just like the name implies shared hosting divides resources amongst multiple sites, therefore if there is a spike in resource from one of the sites your sharing resources with, it directly effects your own. You could switch to cloud hosting, even though its a shared environment still, it is faster (they say 2.5x) than using the standard shared hosting.
EDIT: Also how are your pages setup? Are you displaying a bunch of products per page?
