It defiantly sounds like something else is not working. I've used motion lighting, simple lighting and RM and never seen that much delay.
I remember seeing a break down fo the time RM takes to respond vs running i groovy and for a simple rule like the OP had it should take max 500ms but I might be thinking of something else.
I now use the Room Director app now and the only latency I see is from the actual sensors.
