Stop building SPA, go back to HTML. Re-assess every third party. For extra performance and scaling, implement cache. Relax and see web experience healing.
Especially when trying to buy something. I much prefer to have a longer initial load and then have everything just work instead of waiting as I navigate between pages, the multi stage checkout, confirmation etc.
But yeah, if I'm just trying read a single article on a blog, preloading everything is pointless. A hybrid site with the initial page being server side rendered + progressive enhancement afterwards is theoretically optimal in my opinion.
Ever submit some giant form to get some random error and then lose the entire state of it? Used to be extremely common, even though it shouldn’t have been.
Use the appropriate technology, everything doesn't have to be a SPA.
If that's a connection-less interaction or something small that stays on the same page, sure it makes sense to keep it in the browser. You don't need to build your whole site as a bloated SPA just for few limited use-cases.