Unless you're being targeted as a potential customer or a member of the audience, your mobile performance is irrelevant. What is relevant is that the majority of the devices being used to access sites don't have the performance of mid-high end models.
The common phone is a sub-$100 Nokia or nothing at all?
Even in the US there's something like 10% of people with no cell phone at all, and 50% with "smartphones" which is a very broad spectrum ranging from crap to significant household purchases before considering "data plans" are optional and also range from crap to good.
Even non-phone connection quality can be terrible - I rarely find myself on public or hotel wifi with actually good connections. The difference between 200kb of JavaScript and 10kb can often be measured in seconds.
