test: throttle history verification

loadtest/im-pressure/agent.go

@@ -390,7 +390,7 @@ func (r *agentRun) issueHistoryQueries(ctx context.Context, queries []historyQue
 		return
 	}
 	jobs := make(chan historyQuery)
-	interval := 100 * time.Millisecond
+	interval := 500 * time.Millisecond
 	if r.cfg != nil && r.cfg.HistoryInterval != "" {
 		interval = mustDuration(r.cfg.HistoryInterval)
 	}
@@ -430,7 +430,7 @@ func (r *agentRun) historyPageSize() int {
 	if r.cfg != nil && r.cfg.HistoryPageSize > 0 {
 		return r.cfg.HistoryPageSize
 	}
-	return 50
+	return 20
 }
 
 func missingHistory(recorder *deliveryRecorder, expected map[string]AcceptedMessage) []AcceptedMessage {