Saving local

Enable the option to "Only Download Smart Previews" on the Lightroom Settings>Cloud Storage & Sync tab. If you are importing photos to the iPad, wait until they have been uploaded to the cloud then try using the Clear Cache option (on the Settings>Local Storage tab) which should remove the original files from the iPad and then only a smart preview will be downloaded if you need to edit the file on the iPad.

Be aware, however, that if you export files from the iPad that may require the full original to be downloaded in order to complete the export. But again, using Clear Cache after you've finished should remove the local copy again.