This design should last quite a while with a little care. Don't place it in too warm of area, as the heated house in wintertime can dry out arrangements in a hurry.
Be sure to always keep the water level up in the foam, adding it directly from the water faucet once a day.
Both the greens and flowers will benefit greatly with a frequent misting of a flower sealant.
I use Finishing Touch by Floralife. It seals the flower petals and slow petal transparency. It does the same for the Christmas greens. Don't be surprised if the flowers expire before the greens. I often pull out the flowers as they wilt and replace them with fresh with the greens holding up wonderfully if kept moist and cool.