If you are comparing the speakeasy speedtest to your transfer of the 100MB file the numbers will be different. Speakeasy tests return the results in bits/sec, when you transfer a file the rate is displayed in bytes/sec. So, 15Megabits/sec ~ 1.8Megabytes/sec and 4Megabits/sec ~.5Megabytes/sec see, both tests were accurate, just displayed in a different format.
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If you are comparing the speakeasy speedtest to your transfer of the 100MB file the numbers will be different. Speakeasy tests return the results in bits/sec, when you transfer a file the rate is displayed in bytes/sec. So, 15Megabits/sec ~ 1.8Megabytes/sec and 4Megabits/sec ~ .5Megabytes/sec see, both tests were accurate, just displayed in a different format.