It should be fine since your bag is new and still has the waxy coating. I'd just be concerned once it wears in though because then the leather will absorb the rain easier since the coating wears off and the leather is more exposed. If you have spray, I'd coat it just in case. Doesn't hurt. I spray all of my bags since it takes no time at all and better safe then sorry with any leather bag, it is better to exercise caution.
I wanted to add I'm more comfortable wearing a tano then any other brand in bad weather like snow or rain! For the price, it doesn't really hurt. Tano gets distressed anyway so it sort of blends in if anything does happen. Tano is the type of brand that doesn't look as bad as ruining an $800 bag. I'm not really afraid of exercising too much caution with Tano since it is my ultimate bang around bag. Scratches and dings just add to its' character.
I just have a habit of spraying my bags regardless of the finish though lol