For starters, you will have bubbles. That's a given. The question is what kind of bubbles and how do you minimize their size!
There are several ways to minimize the number and size of trapped air bubbles. The most common is to include a bubble soak (also called a bubble squeeze) at around 1240F. This gives the bubbles time to escape. Half an hour is a typical soak time, but soaking for an hour or longer is preferable for larger pieces. The schedule you suggested has the soak at 1250F with this in mind.
A corollary to the bubble soak is to go slowly from around 1100 to 1240-1250. This also gives bubbles times to escape. Your schedule does this.
Also, it's a good idea NOT to go as fast as possible from the end of the bubble soak (1240-1250) to your fusing temperature. Instead, go around 200-300F dph. This helps with both trapped air bubbles and with the large bubbles that can pop up between the kiln shelf and the glass. Many schedules, including the one you suggest (and, I confess, some I've suggested in the past) say to go AFAP, but I find I get better results when I slow down.
Another suggestion you may want to consider is to sift a small amount of powder between the two layers before firing. This won't work on all designs, but it does tend to leave you with smaller bubbles (so long as you don't overdo it on the powder!). Bullseye has a tip sheet on this:
http://www.bullseyeglass.com/methods-id ... power.html
You can also use beads around the outside of the piece to allow bubbles to escape. The idea, which I learned from Brock Craig, is more advanced, but it will totally eliminate trapped air bubbles. It's covered on page 96 of my book,
Contemporary Fused Glass.
As importantly as any of these suggestions is that you consider the design of your piece and the type of glass you are using. Some designs, such as large frit in between the two layers, are prone to capture bubbles no matter how you fire. Also, smoother glass is more likely to trap air bubbles than glass that's not as smooth.
As for the rest of your schedule, I do have a few comments/questions. I'm not sure why you are holding 15 minutes at 900F. In my typical schedule, I would continue at 300dph to 1100 without a stop at 900F. (Bullseye's schedules, by comparison, usually don't stop at 1100 and just continue to 1240/1250 for the soak. ) But the stop at 900F doesn't make sense to me, and going at 500dph from 900 to 1100 is even more confusing.
The one hour annealing hold should be fine, and going at 100dph to 800 will also work well. (I usually go down to 750, and avoid having to program the drop from 800 to 750, but there's nothing wrong with doing it the way you suggest.)
Finally, I'm not sure why you wouldn't just turn off the kiln at 750 and let it cool on its own. For two layers, no commonly used kiln will cool fast enough to room temperature to thermal shock the piece. But, again, there's no harm (other than the electricity) to program the cool all the way down to 100.
So, to summarize, my basic two layer schedule would be something like.
300 dph to 1100 hold 10 minutes
150 dph to 1240 hold 30 minutes (or longer if you want)
250 dph to 1480 hold 10 minutes (or whatever is the fusing temp that works for you)
9999 to 960 hold 1 hour (or whatever annealing temperature is recommended for your glass)
100 dph to 750 no hold
Kiln off
I'm lazier than you are so I make sure I program fewer steps!
This is my first attempt at firing something this large.