Hibernate model with multiple many-to-many relations slow performance when persisting - spring-boot

Question

We have following schema as described on diagram below. There's an Entity with bidirectional many-to-many relations with two other entities(Relation1, Relation2). There's also many-to-many relation between Entity-Relation2 relationship itself and Relation1 entity. When we create an instance of Entity and persist into database, it's working fine, except that operation takes too much time. I'd like to ask, if there are any possible optimizations on Hibernate level, which could boost performance of save operation.
Here's diagram:
Model definitions:
class Entity : AbstractJpaPersistable() {
var name: String? = null
var description: String? = null
#OneToMany(mappedBy = "entity", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations1: List<EntityToRelation1> = emptyList()
#OneToMany(mappedBy = "entity", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations2: List<EntityToRelation2> = emptyList()
}
#Entity
class Relation2: AbstractJpaPersistable(){
#OneToMany(mappedBy = "relation2", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations2: List<EntityToRelation2> = emptyList()
}
#Entity
class Relation1: AbstractJpaPersistable(){
#OneToMany(mappedBy = "relation1", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations1: List<EntityToRelation1> = emptyList()
#OneToMany(mappedBy = "relation1", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations2Relations1: List<EntityToRelation2ToRelation1> = emptyList()
}
#Entity
class EntityToRelation2 {
#EmbeddedId
var entityToRelation2Id: EntityToRelation2Id = EntityToRelation2Id()
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("entityId")
#JoinColumn(name = "entity_id", insertable = false, updatable = false)
var entity: Entity? = null
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("relation2Id")
#JoinColumn(name = "relation2_id", insertable = false, updatable = false)
var relation2: Relation2? = null
#OneToMany(mappedBy = "entityToRelation2", fetch = FetchType.LAZY, cascade = [CascadeType.PERSIST], orphanRemoval = true)
var entityRelations2Relations1: List<EntityToRelation2ToRelation1> = emptyList()
}
#Embeddable
class EntityToRelation2Id : Serializable {
#Column(name = "entity_id")
var entityId: Int? = null
#Column(name = "relation2_id")
var relationId: Int? = null
}
#Entity
class EntityToRelation1 {
#EmbeddedId
var entityToRelation1Id = EntityToRelation1Id()
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("entityId")
#JoinColumn(name = "entity_id", insertable = false, updatable = false)
var entity: Entity? = null
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("relation1Id")
#JoinColumn(name = "relation1_id", insertable = false, updatable = false)
var relation1: Relation1? = null
}
#Embeddable
class EntityToRelation1Id : Serializable {
#Column(name = "entity_id")
var entityId: Int? = null
#Column(name = "relation1_id")
var relation1Id: Int? = null
}
#Entity
class EntityToRelation2ToRelation1 {
#EmbeddedId
var entityToRelation2ToRelation1Id = EntityToRelation2ToRelation1Id()
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("entityToRelation2Id")
#JoinColumns(
JoinColumn(name = "entity_id"),
JoinColumn(name = "relation2_id")
)
var entityToRelation2: EntityToRelation2? = null
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("relation1Id")
#JoinColumn(name = "relation1_id", insertable = false, updatable = false)
var relation1: Relation1? = null
}
#Embeddable
class EntityToRelation2ToRelation1Id : Serializable {
var entityToRelation2Id: EntityToRelation2Id? = null
#Column(name = "relation1_id")
var relation1Id: Int? = null
}