The two times I've been caught speeding where the officer reduced the fine there was an "R" in the top right corner of the ticket, indicating the speed had been reduced.
I presume if the judge sees this they won't be pleased with you. Is this worth the risk of having the ticket raised to the original speed? Keep in mind, while the insurace companies aren't intersted in a mesely 15 over (with no points!) I'm not too sure they're as lenient with 30 over.
For what it's worth, both my fiance each have a ticket for 15 over (hey, the P5 is fun) our rates haven't been affected.
AKA - Pay the $50.