i've seen a number of these blends.... usually called like "summer cut" blends and such... if it actually is what it says it is, 15 weeks would be one hell of a run. I'd expect you to keep a vast majority of your gains with that time frame since you'll have plenty of time to adjust to the new mass... should be maintainable, assuming everything else is in order.
Bottom line is... its from a UGL, and NOT a pharma company. Yes i know there are tons of reputable UGLs out there that deliver the product they claim to be selling, but there are so many that do not deliver that promise. This is why I stick to human grade...
Maybe i'm lucky in terms of sourcing... but for me it's far easier to obtain human grade than UGL stuff. maybe thats another reason for my preference of top notch gear. Either way... you can't beat human pharma grade... (unless you're getting fakes of course), and with that said, this is my reasoning why I have yet to ever consider using one of these such blends... although the test/mast/tren/sten sounds bonerific just thinking about it... wow, now that would be some good stuff and would save you the hassle of dealing with so many damn vials.
my 2 cents... thats all