The 550 credits per sleeve Level 81+ Nikes i usually play last for 120 hits on each ball.
Since putts don't count, at my current scoring average I get about 54 holes out of each ball or 162 holes per sleeve. At your scoring average of a tick over 66 you should get slightly fewer holes per ball that have the same number of holes per any ball having a life of 120 hits (2.5 durability) .
I play pretty much daily (9 to 36 holes), though it ebbs and flows somewhat, but basically a sleeve of the lvl 81+ Nike balls lasts me 4 to 7 days.
Smooth meter - Make sure you have your computer optimized for playing WGT.