Yeah, 15 ppm should be about right.

Regarding vacation, there are 3 possible options:

1. HiC2 => CYA > 100 ppm & FC > 20 ppm when leaving.
2. 3x doses of polyquat AND removing cartridge from filter OR bypassing sand filter (Polyquat tends to collect on the filter.)
3. Borates > 60 ppm (protects against green algae.)
4. Phosphates < 125 ppb (protects against both green and mustard algae)

Regardless, you want to be sure that your pool is very clean and algae free the week before AND that your filter is in good shape