The lci files are quite large and require some writing on the harddisc but most time consuming is the check of the millions of elements in the files to elements existing already in a database where you want to import into; so, it is better to restore the lci files, and import other databases / zolca files (or also files in other formats) into them. This restoring takes maybe 3 minutes depending on the speed of your harddisc.
When you import into another existing database, so the typically not preferred option, then also memory can be an issue, check in the task manager if openLCA is always running against a memory "ceiling", and if you can increase it.
Hth
