diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2fd5bc51a6d..96837e1df59 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
   * `-cluster.advertise-address` in favor of `-alertmanager.cluster.advertise-address`
   * `-cluster.peer` in favor of `-alertmanager.cluster.peers`
   * `-cluster.peer-timeout` in favor of `-alertmanager.cluster.peer-timeout`
+* [CHANGE] Blocks storage: the default value of `-blocks-storage.bucket-store.sync-interval` has been changed from `5m` to `15m`. #3724
 * [FEATURE] Querier: Queries can be federated across multiple tenants. The tenants IDs involved need to be specified separated by a `|` character in the `X-Scope-OrgID` request header. This is an experimental feature, which can be enabled by setting `-tenant-federation.enabled=true` on all Cortex services. #3250
 * [FEATURE] Alertmanager: introduced the experimental option `-alertmanager.sharding-enabled` to shard tenants across multiple Alertmanager instances. This feature is still under heavy development and its usage is discouraged. The following new metrics are exported by the Alertmanager: #3664
   * `cortex_alertmanager_ring_check_errors_total`
diff --git a/docs/blocks-storage/querier.md b/docs/blocks-storage/querier.md
index e1bfd283781..5e6351b5a78 100644
--- a/docs/blocks-storage/querier.md
+++ b/docs/blocks-storage/querier.md
@@ -387,7 +387,7 @@ blocks_storage:
     # enabled), in order to look for changes (new blocks shipped by ingesters
     # and blocks deleted by retention or compaction).
     # CLI flag: -blocks-storage.bucket-store.sync-interval
-    [sync_interval: <duration> | default = 5m]
+    [sync_interval: <duration> | default = 15m]
 
     # Max size - in bytes - of a per-tenant chunk pool, used to reduce memory
     # allocations.
diff --git a/docs/blocks-storage/store-gateway.md b/docs/blocks-storage/store-gateway.md
index fb873f1b07e..32961dd9de4 100644
--- a/docs/blocks-storage/store-gateway.md
+++ b/docs/blocks-storage/store-gateway.md
@@ -434,7 +434,7 @@ blocks_storage:
     # enabled), in order to look for changes (new blocks shipped by ingesters
     # and blocks deleted by retention or compaction).
     # CLI flag: -blocks-storage.bucket-store.sync-interval
-    [sync_interval: <duration> | default = 5m]
+    [sync_interval: <duration> | default = 15m]
 
     # Max size - in bytes - of a per-tenant chunk pool, used to reduce memory
     # allocations.
diff --git a/docs/configuration/config-file-reference.md b/docs/configuration/config-file-reference.md
index cdee3edc540..d0754cf38b2 100644
--- a/docs/configuration/config-file-reference.md
+++ b/docs/configuration/config-file-reference.md
@@ -3799,7 +3799,7 @@ bucket_store:
   # enabled), in order to look for changes (new blocks shipped by ingesters and
   # blocks deleted by retention or compaction).
   # CLI flag: -blocks-storage.bucket-store.sync-interval
-  [sync_interval: <duration> | default = 5m]
+  [sync_interval: <duration> | default = 15m]
 
   # Max size - in bytes - of a per-tenant chunk pool, used to reduce memory
   # allocations.
diff --git a/pkg/storage/tsdb/config.go b/pkg/storage/tsdb/config.go
index 0c6920575b9..eaf1e614059 100644
--- a/pkg/storage/tsdb/config.go
+++ b/pkg/storage/tsdb/config.go
@@ -243,7 +243,7 @@ func (cfg *BucketStoreConfig) RegisterFlags(f *flag.FlagSet) {
 	cfg.BucketIndex.RegisterFlagsWithPrefix(f, "blocks-storage.bucket-store.bucket-index.")
 
 	f.StringVar(&cfg.SyncDir, "blocks-storage.bucket-store.sync-dir", "tsdb-sync", "Directory to store synchronized TSDB index headers.")
-	f.DurationVar(&cfg.SyncInterval, "blocks-storage.bucket-store.sync-interval", 5*time.Minute, "How frequently to scan the bucket, or to refresh the bucket index (if enabled), in order to look for changes (new blocks shipped by ingesters and blocks deleted by retention or compaction).")
+	f.DurationVar(&cfg.SyncInterval, "blocks-storage.bucket-store.sync-interval", 15*time.Minute, "How frequently to scan the bucket, or to refresh the bucket index (if enabled), in order to look for changes (new blocks shipped by ingesters and blocks deleted by retention or compaction).")
 	f.Uint64Var(&cfg.MaxChunkPoolBytes, "blocks-storage.bucket-store.max-chunk-pool-bytes", uint64(2*units.Gibibyte), "Max size - in bytes - of a per-tenant chunk pool, used to reduce memory allocations.")
 	f.IntVar(&cfg.MaxConcurrent, "blocks-storage.bucket-store.max-concurrent", 100, "Max number of concurrent queries to execute against the long-term storage. The limit is shared across all tenants.")
 	f.IntVar(&cfg.TenantSyncConcurrency, "blocks-storage.bucket-store.tenant-sync-concurrency", 10, "Maximum number of concurrent tenants synching blocks.")