For a reduction of this order they will have to go back to the creditors to see if thy will accept the reduction. This might result in a small extension rather than failing the IVA.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014
Fingers crossed for you - your creditors would receive less in Bankruptcy so here's hoping they see the positives about your reduced payments - but as others have said it may mean an extra few payments to ensure you still reach the required dividend
Sharing from experiences of dealing with debt
There is a solution for everyone .... Just need to stay positive !