Curious as what you mean by a 1.5gph default? The nozzle/emitter defaults in Rachio are specified in “in/hr”.
If you’re interested in looking a bit deeper into what is recommended here in Phoenix, and how those recommendations can be made to work with Rachio Flex, take a look at this post. If nothing else, download the spreadsheet and look at the ‘Water-Use-It-Wisely’ information. My concern is that for shrubs you should actually be watering more deeply than you are now, rather than multiple times a day. Adding a second watering my not save your shrubs. Again, the ‘Water-Use-It-Wisely’ is pretty easy to understand and an easy to understand resource.