WordPress plugins can be great for adding features to it, but needing so many plugins suggests that they are being used to change WordPress into something it is not optimized to be. IMHO, the ideal approach would be to find something closer to what you are trying to change WordPress into.
If you absolutely must use WordPress and eCommerce, there are things you can do that could help some.
The usual things like combining files to minimize HTTP requests, optimizing images, using a CDN, minifying / compressing files, replacing db calls in templates that get unchanging values, etc.
I have a feeling a main cause of the problem is the plugins. The only way I can think of to make improvements is to systematically run speed tests with various plugins enabled / disabled to identify which are the bottlenecks and then change the way they work or find better replacements for them.