Is the Redis cluster installed in k8s have less performance compared to installed standalone?
As already mentioned by Burak in the comments you can choose to have a dedicated node(s) only for the Redis pods in order to avoid resource sharing with other services.
Also it is worth to mention that Redis performance is tied to the underlying VM specifications. Redis is single-threaded so a fast CPUs with large caches would perform better. Multi-cores do not directly affects performance. If your workload is relatively small (objects are less than 10 KB), memory is not as critical in order to optimize the performance.
Finally, you can use the redis-benchmark in order to test the performance yourself. There are plenty of examples to check out. Or use other tools like memtier_benchmark or Redis Memory Analyzer.