It depends. If one database needs more IO than the other then no, you’ll just make things worse by giving that database less disks.
Usually you want to give the databases the most disks possible. Is your IO mostly reads or writes? If it’s writes then stick with RAID 10, however if it is mostly reads (like 99% of databases are) then try switching to RAID 5 as you’ll have more disks available for reading.
When using RAID 10 you only get access to the performance of 1/2 the disks. With RAID 5 you get access to all the disks (or all but one depending on the way the RAID 5 is done).