Pages has always been slow to open and it is getting worse with each new update. I have an M2 Mac Mini Pro w/32 GB RAM running Sonoma 14.6.1 and I certainly don't wait 5 minutes for a 2 - 4 page document to load though it is more like 15 - 20 seconds which is still slow.
The only thing you can do is not attempt to open a Pages document right after booting your Mac as several System housekeeping tasks are competing for resources: Spotlight, Software Update, potentially Time Machine, and other activities — which may last 10 - 15 minutes.
If you leave several large applications open and with 16 GB RAM, you may be running low on memory and forcing the operating system to page (run slower) while Pages is attempting to launch.
If you are attempting to load a document in Pages that is stored on iCloud, you are at the mercy of Internet propagation delays between you and Apple's Servers. Same drill if another cloud service.
Do not run any anti-virus from any vendor as that will adversely impact operating system and application performance while providing nothing but false positives.