The label on your foundation bottle says SPF 15 – is this enough to wear alone, with no additional sunscreen??
Well, yes – and no…..
Sunscreen in your foundation or powder is a great idea but it isn’t something you should rely on. On darker days or when you are not going to be outdoors for very long, an SPF of at least 15 in your makeup should be fine, otherwise – it’s best to supplement it with something else.
Most people will not apply enough of the makeup product, or cover their whole face substantially, so you would not get complete protection. And makeup tends to wear off throughout the day – through sweat and even having it rub off on hands and 
clothes.
Another common misconception people have is that if they have applied an Oil Free Moisturizer with an SPF of 30, then a mineral foundation with an SPF of 19 over top, they have created an SPF of 49. Not true. This is not a bad idea – in fact it is great that you are keenly applying SPF and your skin should stay mostly protected – however you are still only getting the SPF protection of the higher level of product – not the two combined.
So, do not stop wearing makeup with SPF for the extra protection – but please do not forget to use an SPF moisturizer first!