150Mbps = maximum speed of 18.75MB/s.
To say that's slow is being generous.
A wired gigabit connection will give you 128MB/s.
I'm 99.99% sure that your issue with media streaming is a network thing, not a NAS one. Do you know what standards your Wifi router supports?
If you buy a NAS from Synology, QNAP, et al you're paying for the software and the branding than anything else. Especially when it comes to home apps like media players and such. And "Well tested solutions" aren't immune from user mistakes, errors and general SNAFUs.
As a disclosure, I work for a major NAS company. And with that said I plan to build a DIY FreeNAS myself later in the year.
Don't get me wrong though, pretty much any NAS on the consumer market right now will serve you well. It just comes down to what else you get that justifies the cost (with timely technical support being the No. 1 factor in my book.)