Switch DABlockTime to 15 seconds (cosmos#1188)

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## Overview
Closes: cosmos#1180 
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block/manager.go

@@ -29,7 +29,7 @@ import (
 )
 
 // defaultDABlockTime is used only if DABlockTime is not configured for manager
-const defaultDABlockTime = 30 * time.Second
+const defaultDABlockTime = 15 * time.Second
 
 // defaultBlockTime is used only if BlockTime is not configured for manager
 const defaultBlockTime = 1 * time.Second

config/defaults.go

@@ -22,7 +22,7 @@ var DefaultNodeConfig = NodeConfig{
 	LazyAggregator: false,
 	BlockManagerConfig: BlockManagerConfig{
 		BlockTime:   1 * time.Second,
-		DABlockTime: 30 * time.Second,
+		DABlockTime: 15 * time.Second,
 		NamespaceID: types.NamespaceID{},
 	},
 	DALayer:  "mock",

da/test/da_test.go

@@ -33,7 +33,7 @@ var (
 	testNamespaceID = types.NamespaceID{0, 1, 2, 3, 4, 5, 6, 7}
 
 	testConfig = celestia.Config{
-		Timeout:  30 * time.Second,
+		Timeout:  15 * time.Second,
 		GasLimit: 3000000,
 	}
 )