Not having that problem but usually cleaning up a few things helps with that... The S10 is a pretty powerful device and it would probably take a ton to choke it up, but how many messages did you import? >10k <10k <50k? If you imported high numbers or a lot of MMS messages try reducing the number of messages. Use the cache clear function in the app details about the messaging app, this won't delete any messages but it will get rid of junk the app may be holding, and go to Device Care in the setting menu and optimizing. You could also bring in a ringer by getting CCleaner from the Play Store, but the other two should take care of it pretty well. Restarting your device every few days is also a good health tip for keeping things running smoothly.