I'm sorry but I'm finding it hard to make your numbers add up!
The interest you pay depends on your outstanding loan balance.
The quicker you pay off your outstanding loan balance the less total interest you will pay.
So if you can afford to pay more off your outstanding loan balance now you will have paid less interest over the full term.
I think saving up to pay off a lump sum is probably not the best idea if you are trying to cut costs!
Can you walk in and ask for a lump sum to be applied to principal repayment?
Usually CU's initially deduct the interest due from any payment and apply the balance against the principal. That would mean if you have been making regular repayments your interest would fairly up to date with only weeks/month due (at max interest 10k = €100 interest per month)
They would be stupid NOT to accept a lump sum off the principal
if the other option was not to get a lump sum at all!
They may argue that they are entitled to apply any payment to interest first!!!
what implications could arise?
They may ask you where the lump sum came from!
Loan is murdering me on top of the mortgage...
Go and make an appointment with MABS. They can help!
You could ask the CU to apply some/all your shares against the loan balance outstanding. It is a bit of a neuclear option and depending on your age it may not be the best option.
HTH