Read my Guide for a great method of rinsing Flourite.
Your plan is doomed. If the gravel is larger than the Flourite (and pea gravel is) then the Flourite will end up on the bottom and the pea gravel on top.
And 15 lbs (one bag) of Flourite and 10 lbs of gravel is not enough. You will need at least 25 lbs of gravel (that's the voice of experience in this whole post).