i have an interest only mortgage but no savings to pay it off in 15 yrs what is the best savings plan

This is difficult to say to be honest m2parr, as you've got 15 years until you need to pay it off you might want to look at investing rather than saving as they usually do better over the long term, but they're not risk free.

ISAs and fixed term savings accounts are likely to be worth considering as well as you won't want to access the money for 15 years.

If I were in your shoes I'd speak to an IFA to discuss your options.

thank you for taking the time to help with my question, much appreciated