DT RR 1.1 / 415 ERD is 599mm
Open Pro is ERD is 605mm (it’s listed as 602mm but Mavic measure funny and don’t include nipple bed so you need to add 3mm 🙄 )
The actual poke length difference will depend on the hub, more so if you have particularly odd hubs with extreme spoke angles involved ie: very big flange etc. but assuming ‘normalish’ size hubs the spoke length difference is likely 3-4mm shorter on the DT rims
Throw the details into some online spoke calculators (EDD, or the DT one etc.) and have a play to confirm, but probably pushing it to try and re-use your spokes, whichever way round you’re swapping as you’ll either be too short or too long for the new rim.