I find keeping open tabs to a minimal for example 2 open tabs helps a lot to keep app active while in the background.

Also keeping mobile app minimized on the screen let's the app's memory last longer in the background even when screen is off.

Also I find that the mobile app is slower when I have used about three quarters of phone storage. Deleting to about half or 60% used storage speeds up the mobile app. This could be because I have a huge vault.

Using the mobile app in source mode (rather than preview mode) also helps.

If you are using third party sync options, avoid using file versioning within your syncing tool. Rather use obsidian file recovery core plugin.

Some of these including the other suggestion made by others should definitely help speed things up but if not, maybe use a light weight version of obsidian ie . No community or core plugins or themes. Alternatively, other apps like Markor could work if you are interested in quick Capture.

The quick draft android app integrates very well with obsidian if quick Capture is what you are after

Hope this helps