Similar experience as @RudolfAtRTC. Fairly old CPU (however no slough) Windows 10, very average mechanical hard drive.
Start after overnight shutdown (Windows cashing cleared) takes about 30 seconds to show splash and then another minute before displaying last used sketch and ready for editing. If shut down and restarted splash in about 5 seconds and ready after another 30 seconds.
Using File->Open takes about 25 seconds before ready (thankfully we are spared the splash when using Open).
Some reports of unexpectedly long startup times are tracked here:
As someone who does a lot of beta testing, which seems to often consist of restarting the Arduino IDE over and over again, I know very well the pain of starting at that teal splash screen for what seems like an eternity. But my startup time is on the order of seconds, not minutes. My PC is nothing extraordinary, mostly running Windows (which has historically been the poorest performing OS), and with an unusually large number of sketches, libraries, and boards platforms installed for it to churn through.
The developers are also not afflicted with these mysteriously long startup times.
So it could definitely be helpful if the community can determine what is different with their system to cause the unexpected results.
You might get some insight by running the Arduino IDE from the command line and then checking the output that is printed by it there for anything significant. I can provide instructions if needed. Just let me know and also your operating system.