Is an Index Linked Isa the best way to raise funds to pay Interest Only Mortgage?

Nezpz

I am wondering if I should continue with my mortgage ISA Plan. It is index linked and includes critical life cover- been paying in for 19 years. The fund value is currently £18,000 with £12,000 left to raise.
I have 6 years left on my interest only mortgage and, as it stands, about £12,000 left to raise in the fund. The final fund value is dependant on the investment growth so is not guaranteed. At the moment it's just about on track for the required £30,000.
My question is: should I leave things as they are or withdraw the money from the fund and find an alternative way to pay/save for the final £12,000. 
The fund value is nearly £18,000. Would this money be best used to pay of part of the mortgage or saved elsewhere??
Every few years I mull over the same debates and then just carry on as usual but I would really appreciate some second opinions.
Thanks for reading

Whats_your_forte

Sorry but doubt anyone can answer this based on just these variables. We have no idea of your capacity for loss, risk profile, age, earnings etc

But if you are saying it has taken 19 years to get to £18k and has 6 more years to get another £12k, then you might have answered your own question. But seek some individual advice on this

Nezpz

Thanks for your reply.
Yes, I didn't want to bore anyone to tears with all the facts. I guess that is the gamble and consequently it's the very thing that I'm trying to weigh-up. How will the fund perform?? 
The plan was originally sold to me with an assumption that if investments grow at 7% a year then the target figure of 30,000 will be reached. Who knows what the future holds though!
regards

Whats_your_forte

You are doing the right thing. You'd rather know now rather than find out in 6 years.

Just get some projections from the provider on the ISA along with a repayment mortgage quote for the shortfall (allowing for the fact the ISA payments will cease)

Nezpz

Thanks again for your time. I'll do both.

Thrugelmir

What rate of interest are you currently paying on your mortgage? Have you considered overpaying your mortgage? 

Nezpz

Hi, I’m not sure if that’s an option on an interest only mortgage. I think I need to have a good chat with someone in the know. It’s worth considering-thanks

dimbo61

Most if not all mortgages allow overpayments even when in a fixed rate deal.
We have No idea what interest rate your paying on the mortgage or return your getting from your ISA but if you have no other expensive debt and that Emergency fund of 3/6 months of Income then overpay if possible.