You don't say how the devices are connected to your Sky router, nor what you mean by slow, nor really anything that would be useful in diagnosing the problem and so it is difficult to help other than in a general way.
You may just have a slow connection between your router and the local exchange. This may or may not be fixable e.g. you may just have long line and nothing can be done about that.
You may be on Sky Connect product which tends to be "slow" at peak times. Nothing can be done about that either except to move to another ISP.
You may have problems between the devices and the Sky router especially if you are using WiFi. That is a massive subject and so you should search on using a tool called inSSIDer to help there.
As to what is "slow", it's a matte ofd opinion really and you need to ensue that you are not mixing "b" = bits with "B" = bytes *8 bits). Line Speed tends to be measured in bits per second (b/s) but devices like PCs tend to use bytes per second (B/s).