Another thing to try, before setting up sync, is changing the "Attachment behavior" from "Always" to "Automatic" or "Manual" (see Feature suggestion: Mobile: Change default attachment download behavior from "Always" to "Automatic").
Changing from "Always" to one of the other options means that an initial sync will not try to download attachments (just notes, tags, notebooks, attachment metadata, revisions, ...).
This may make an initial sync faster.