Exactly how I would write this as far as the blinds go.
I am not super keen on dropping levels to 15 minutes unless you get past the 20BB in play point.
Assuming 20 players as written you probably fit 5 hours. (Not counting breaks.). But personally, I would probably drop the starting stack to 10-12k rather that drop the level length to 15 minutes that early in the tournament.
How many players are you expecting? Do you have reentries?
Late edit for some alternatives:
You could drop the 800-1600 level and keep that group at 20 minutes each. Or you could keep 800-1600, change 1000-2000 to 1200-2400 and drop 1500-3000, and restart at 2000-4000 after the color up.
But again, I may just be picking nits here. But I find these alternatives preferable to 15 minute levels where I would assume the tournament will still be full handed.