New Mac user, why is it so slow!?

I made the transition from Windows to a Macbook Pro (early 2015 model) last week.

First of all when I initially turned it on I noticed it was significantly slower than my 3 years old Windows laptop with an SSD drive, I just figured it was doing it's thing as it's a new computer but each time I turn it on it takes an age.

Everything seems to be very laggy and it likes to just randomly freeze all of the time. The battery life is no where near the 10 hours Apple claims (2-3 hours when internet browsing) and the memory usage is 7GB just using Safari!?

Also the internet is painfully slow despite having a fibre connection!

Is it just my Mac that's screwed or is it from the new Yosemite update?

All of the above was when it was fresh out of the box and NOTHING else installed on the machine.