I believe 150± is too much even for dense maps like the UK. I know that your client has probably already downloaded audio files and much of the map already, but please don't forget to report back here with your findings.
Providers are notorious for their usage statistics. At least here. Sometimes I buy a package and check my balance to find 40+ mb has already been used! Sometimes it reports a number now and when I check again hours later it gives a smaller number. I KNOW they are actively cheating, even if unintentionally by their buggy billing system, but their word is the law when it comes to usage
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