Actual percentage increases:
L1 25/50
L2 50/100 = 100% increase
L3 75/150 = 50%
L4 125/250 = 67%
L5 200/400/400bba = 167% (60% sb/bb only)
L6 300/600/600bba = 50%
L7 400/800/800bba = 33%
L8 600/1200/120bba = 50%
L9 1000/2000/2000bba = 67%
L10 2000/4000/4000bba = 100%
L11 3000/6000/6000bba = 50%
L12 5000/10000/10000bba = 67%
L13 8000/16000/16000bba = 60%
L14 15000/30000/30000bba = 88%
L15 25000/50000/50000bba = 67%
L16 40000/80000/80000bba = 60%
A few levels stand out as outliers: L2 (100%), L5 (167% !!), L7 (33%), L10 (100%), and L14 (88%). The rest are all within a narrow range of 50% to 67%.
With 9 players, expect the tournament to last no longer than a 7500/15000 blind level, and no longer than 14000/28000 for 17 players. With 20-minute levels, that means 13-14 levels = 4:20 to 4:40 plus breaks, but likely finish a couple of levels sooner.
Personally, I'd add a 200/400/no bba level between L4 and L5, replace L7 ànd L8 with 500/1000/1000 and 800/1600/1600, and replace L9 with 1200/2400/2400. Those changes will not dramatically alter the length of the event, but they will have an effect on how the tournament feels in terms of pace.