It is indeed a little slow – you seem to have a pretty full calendar with a high number of recurring events. Can you provide any rough figures as to how many events are currently on the system and how many/what percentage might be recurring in nature?
What about the hosting environment – can you provide any details on that front?
We are working progressively toward creating a leaner machine under the hood, you’ll be pleased to know, right now though good use of caching (including query caching) is definitely a worthy strategy.