How fast do i really need my internet to be?

So to start things off I I live in LA fairly close to a time warner building naturally they became my internet service provider not to long ago, I live a medium sized apartment my current subscribed speed is 15 mbps but in speed tests I top out out 9-11 I have 1 MacBook pro, iPhone 5, playstation connection to one router, my questions are:
1. Is 15 mbps enough for 1 computer to quickly browse youtube, check mail, Netflix simple stuff?
2. If I upgrade my router to the new AC Wi-Fi standard along with my new MacBook that supports the new AC Wi-Fi standard while running 15mbps will I notice a difference that's worth 200$? Lol
3. How can I boost my Wi-Fi to reach my 15mbps?

15Mbps is more than enough. I had 6Mbps and never had problems (I upgraded to 12Mbps though, because I was downloading more stuff off of Steam)

Upgrading the router would be worthless, especially if it costs you $200

And while you pay for 15Mbps, that's just your maximum. Actual speeds can fluctuate depending on how many other users there are, time of day, and other various factors.

Either way, Anything over 8Mbps is fine for pretty much everything.

Well just be grateful man, my internet is about 2mbps in speedtest and i have to pay $30 per month…

Wi-Fi can easily hit 15mbps so the slowest thing listed is your ISP internet. Only way to make it faster is to pay more monthly or look for a better competitor with say Fiber internet.

Simple situation you are in. The numbers are not going to be exact from what ISP says it is. ISP = TimeWarner.

And that is fast enough for everything but Netflix maybe cutting it close if you watch in HD quality

Check your speed directely with your router with just one pc, if the speed get 15, the problem with you lan network. If not, restart your router, if not get the correct speed, call the service provider to check speed connection between your router and the ISP. May be using some tools.