Need help with understanding pattern

How-to Questions
1

its says

Keeping rib correct, dec ( as in 15th round) in next and foll 6th round/s until 66 sts remain.

When it says foll 6 round/s until 66 sts remain… do I make the decreases as per the instruction for the 15th round 6 times straight? or do I do the decreases per instructions the 15th & 16th round 6 times straight?

16th round is just knitting the rows after the 15th row decrease 4 times.

2

you dec every 6th round --as in round 15
1
2
3
4
5
6 dec
7
8
9
10
11
12 dec
you do this until there is 66 sts left