Your best option probably is to hide this with a loading screen. You can also create them in batches, e.g. create 100 sprites every tick, which will create overall 6000 sprites in a second at 60 fps. You might still wanna hide that behind some transition/loading screen but it should at least mitigate some of the lag.
Are you by any chance trying to do this on mobile btw? Because I can spawn 5000 sprites practically instant on my PC. It's a beefy one but still, 5-15 seconds freeze I can see happening on a phone.