I'd say your coil lifespan sounds about right for how much you vape.
My gf uses stock coils (Geek Vape Supermesh) and goes through them at a rate of around 3 days per coil too.
I use mesh RTAs (specifically the Profile Unity - no leaks ever, great flavour, easy to wick with the right cotton) and get between 4-7 days before needing to change, occasionally longer. I do vape
very sweet liquids though (mainly dessert/bakery flavours).
As for Dispergo, they're very nice flavours but I found them to be absolute coil destroyers.
Loads of blue rasperbby flavours here (you can ice shots if they're not "cool") -
Vaping101.