I expect that you might have a single Node entity class in your Spring Boot solution and that your are using dynamic labels (@Labels())
I expect that saveall uses a merge for each node that it creates. Creating an index on id will solve your performance problemen. Performance now decreases each time that you call saveall, (Also see @Properties(prefix="node",delimeter="_", allowCast=true for creating a dynamic properties collection)
Node is here the Node entity class. (Issue that i see in Neo4j browser is that is shows total count for Node (my entity class) and the totals for each dynamic label,
CREATE INDEX ON :Node(id)
Creating the index solved the performance issue for me. Saving 5300 Nodes and about 3000 Edges now each time in < 2s. Without the index 10s increasing after each saveall 20s, 35s, ......