Web Interface on the Raspberry Pi
If the frontend will run on a browser executed on a laptop o desktop it will run fine, but if the interface will run on a browser executed on the Pi maybe it will be too expensive in terms of GPU/CPU usage and it will require fine tuning in order to avoid unnecessary re-renders.
So if the browser is on a remote machine ok, if not think about a something like TkInter for UI.
I have a web application that I developed for use on a Raspberry Pi written in Python and hosted on nginx.  It's a bit slow to serve new pages, even when there is very little to no logic being processed for the page that's loading (4-5 seconds+). 
I know that's a common problem as Pi's aren't exactly equipped to handle the load required to deliver web pages super quickly, but I was wondering if anyone had any experience with this and if it would be worthwhile to recreate the app in some other environment?  I was wondering if perhaps a nodejs server would be significantly (a few seconds) quicker in general, or building a single page application using react would be worthwhile? Or if there is some other solution that would be even faster?
EDIT:
more info: raspberry pi 3, json for storing/reading data (very small amounts of data), running chrome, only one user interacting directly with the app, and on the device itself (not from the internet or another network)