Signature posts will be counted at the end of the campaign, at that time you need to have an average of 15 posts/week. It doesn't matter if you have 10 in the first week and 20 in the second or the other way around, you just need to have 30 posts to receive stakes for both weeks
The rules are written:
Rules, Terms Conditions:
1: The Signature should be kept until the end of the ICO, removing the signature before that time will result in a diqualification.
2: During this period you must make a minimum of 15 Posts in order to be considered eligible.
Everything is very clear until the end of the ICO, you need to write at least 15 posts . In terms of there is no division into weeks.