Most importantly, does your BB cream get rubbed off? the thing is moisturizers are suppose to sink into your skin, so they don't disappear or move around or get wiped off during the day, which means the area you covered with SPF are protected with SPF. For make up however, if they come off, their SPF comes off of course, then you are unprotected.
If your BB cream doesn't bulge, it should be ok. The general rule is you MUST wear spf 15 or higher, but no need to go above spf30 unless you are super pale or burn easily.You MUST look for something that protect against UVA and UVB, also termed "broad spectrum". Lastly, spf loose its effect after 2-3 hours. I work in an office so I figured that since it take me 10min to walk to the car and 2min from car to apt, 12min of unprotected sun should be good for vitamin D without burning. But if I plan to spend time outdoors after work, I apply a light layer of sunscreen over the T-zone and cheeks, basically areas that are easy to burn.