I don't know the details of your app, but I have a feeling that there are many places where you can optimize it.

You can't just take a desktop app and stick it on the phone. It will perform poorly.

But you have to design mobile (web) apps from the ground up relying on the strengths of the mobile platform.

One idea is to limit the functionality of the mobile app. Tasks which are very UI heavy should probably be simplified or removed.