One option would be to only grab context STATE, CREATED, ID, and UPDATED from the feature until the user actually clicks on a specific job but this would require extensive changes to ImportDataPage and supporting UI classes. Another option may be to implement a faster XML parser here? (Not sure what options already exist for this in GeoServer)
Medium
The slowdown appears to be occuring here:
https://github.com/geoserver/geoserver/blob/4be37806e114120510c419987f11cadafa3aa64b/src/community/importer-jdbc/src/main/java/org/geoserver/importer/jdbc/ImportContextMapper.java#L66
One option would be to only grab context STATE, CREATED, ID, and UPDATED from the feature until the user actually clicks on a specific job but this would require extensive changes to ImportDataPage and supporting UI classes. Another option may be to implement a faster XML parser here? (Not sure what options already exist for this in GeoServer)