I would not totally ignore the disk queue length since this is a local array. However a 15 second sample interval is way too long an interval - to diagnose real issues you'll have to get down to every second. The 15 second sample interval is almost an eternity.

The 'old school' formula for raising the 'red flag' of concern is:

# disks in the array * 2 is your warning threshold at a high level. so your 2.93 average is below the threshold for pain of 8.

However the other information posted is valid as well. I would concentrate on actual read and write queue lengths for internal disk arrays.