Ross has a good point, but you tagged this topic with Z-Wave, so I assume this is the technology you are using. I have rules that update dozens of Items and the Z-Wave binding has handled it perfectly. However, you may have some issues in your network that could cause slowness. I suspect this is the cause of your issue.
- How many devices do you have in your network? Have you looked into the debug log for the binding? Are devices slow to respond when manipulated through the UI?
- Do you have any ghost nodes (nodes in OH without physical devices assigned to it)?
- What else is running on your system other than OH? This can significantly slow things down.
- How often are you using the rules? If not used for a while, they could be getting reloaded, which can cause some slowdown when executing. This would not cause massive slowness though, unless your rules are using a lot of primitives.
That said, the rules DSL is abysmal, and I highly recommend scripted automation. Take a look here for instruction…
https://openhab-scripters.github.io/openhab-helper-libraries/index.html
… and here for a simplified installation for Jython…
If you wait a few days, the libraries will be updated and the installs will be in Eclipse Marketplace, so 2.5.x users will be able to install them through the UI. There will also be add-ons for Groovy, jRuby, and Kotlin.