There are 2 things preventing you from being able to upload videos over 15 minutes:
#1) Content ID Claims are not in good standing. To fix you must delete all videos that are blocked globally.
#2) As long as you have any Copyright Strikes you won't be able to upload videos over 15 minutes. If you receive no additional copyright strikes for the next 6 months then 1 copyright strike may (ie might) be forgiven.